Hi mate,
I'll weigh in with some thoughts. I'm not personally a Jimny owner but we have (and have had) several in the club. I'd recommend you come along to the tech weekend which is in three weeks - a lot of this stuff is a lot easier to demonstrate and discuss than to explain on here.
I'll work though your list, however, the overriding thing to consider when working with a Jimny is that the cars don't have very much payload. Anything you add to the car (including fuel, water in the washer bottle, and those floor mats and cross bars) reduces your payload. Overloading the car reduces its offroad and on road performance, and, critically, reduces the reliability of the vehicle.
Other than your list, these are the things I'd be fitting straight away.
A compressor and tyre deflation/inflation kit
Tyre levers
Extended diff breathers
First aid kit and fire extinguisher
Then, more substantially:
215/75/15 off road tyres of your choice, these go on standard rims and require little to no other work to install
A hand winch
A bolt in 2" suspension kit like an OME kit, mostly to improve performance when loaded.
A rear differential lock such as an ARB air locker.
A cargo barrier behind the front seats.
To go out on my own and get to locations I couldn't make in my CCC
I would very strongly advise against this, at least until you are very familiar with your vehicles capabilities and are very proficient with self recovery. Despite almost 25 years of driving offroad, going anywhere that requires low range by myself (single vehicle) makes me very nervous. That's why I'm in a club and I basically never go 4WDing without other cars with me. The number of people we have encountered over the years out by themselves that require assistance is very surprising.
- Steel rims (preferably 17") with A/T tyres
There's no reason to run 17" rims - the only offer disadvantages at small tyre sizes. Improving traction when off road is all about reducing tyre pressure to allow the tyre to conform to the terrain. With standard tyres, a Jimny already has a tyre that's quite low profile (short sidewall) moving up to a taller rim will only make this problem worse. Stick to a 215 75 15 tyre which is about 2" taller than your current tyres, (but still legal) This allows 1" more sidewall to deflect to improve traction, is a readily available size, and fits on your standard rims. If you wish to retain your road tyres and alloy rims for road use, you can fit 215 75 15's to standard steel Jimny or leaf sprung Sierra rims which are easy to find and very cheap.
I don't see the point for AT tyres if you aren't daily driving the car. the performance difference off road between AT and MT tyres is substantial, and if you're not commuting with the car the increase in road noise isn't much of an issue.
- Some sort of bull bar, hopefully light weight
If you are planning lots of travelling at dusk or dawn I completely agree with the idea of adding a (strong) bullbar. If you travel is mostly in the day I'd move it down the list. The stock plastic bumpers are light, and absorb a surprising amount of impact. The current trend of running without bars around the headlights makes the added protection of these styles of bullbar for animal strikes pretty limited - if you hit a roo at dusk and it takes out your headlights despite your bull bar, what was the point of the bar? you're still sitting beside the road needing a tow.
I guess I'm suggesting really critically analysing the need for any accessory, and weighing up what's an accessory and what's actually required. For example, a compressor is required to get the most out of your tyres. A bull bar isn't required to do anything if you're not travelling when/where animal strikes are likely.
- Probably a snorkel just in case
If you feel like it, but you should never be driving into anything remotely near the depth a snorkel is required for by yourself. When assessing water depth, don't assess whether it requires a snorkel or not, assess how bothered you'd be if the water was that depth inside the car. If the idea of 6" of water inside the car is impossible to consider, then you shouldn't be going anywhere that requires a snorkel. Snorkels are great and all, but if you have to stop because you've become bogged or rutted out in a crossing, and/or have to reverse, the car WILL fill wither water. It's inevitable. Also, theres not currently a snorkel made to fit a late model jimny - some adaption is required to the pillar brackets to adjust the fit for the different guard profile.
- A little ~2 tonne bull bar mounted winch for emergencies
I don't believe this is a good idea. A Jimny used for one-up travel when laden requires a 6000lb winch in my opinion. There are a lack of quality, large frame (standard Warn mounting pattern) 4500lb winches on the market, as they are predominantly designed for ute tray mounting or UTV use, not for vehicle recovery. The small frame winches have smaller brakes, less rope etc and are lighter, but will struggle to pull a Jimny thats, for instance, on it's diffs and unable to assist the winch at all. I dislike electric winches, I think they impair decision making, especially when you're travelling alone. I think hand winches are great. They're very versatile, but because they're slow to set up and use, you'll drive the car in a way to avoid needing it. This is safer than driving into situations because you know you can winch out and then finding the winch kills your battery/doesn't work/you break the rope/you can't find the hand control/it melts the battery terminals off the battery/the winch brake fails and you slide back down the hill.
Just sayin'
Rack on the back with an extra fuel can
This is illegal. Petrol cannot be carried on the rear of the vehicle in a jerry can holder. It's also a way to add a LOT of weight and complexity (the rack will need to be a swing away as the rear door can't take the extra weight) to gain a small amount of range.
- Something to chop through fallen trees, probably a bow saw
Sure. Good call.
- Aluminium roof cargo basket
Not a fan of any roof load at all on Jimnys. The centre of gravity is already pretty high, and even a seemingly small amount of weight has a significant effect when it's that far above the cars COG.
- Window tinting (for glare and heat not looks)
Sure
- Basic recovery kit of snatch strap, skids and med kit (and whatever else the kit comes with!)
Sure. Also, Jimny's don't really have adequate recovery points front or rear. I believe there are sources for bolt on recovery points that a far more robust than the factory tie downs.
It'd be great to get a little more performance out of it cause it does struggle on steep tarmac but from what I can tell there's nobody who does this sort of thing specifically for Jimny's so a custom fit out of a turbo or supercharger probably isn't realistic?
No there isn't. CAPA in SA might have offered a supercharger at one point but I don't know if anyone fitted one or if they are available for the 2015 car. The more common upgrade is a larger M series motor from an 1.8 Ignis, 1.6 swift etc, but the cost of this swap using new parts (to match your brand new car) would be prohibitive. I'm also not aware of anyone that has done this swap and had 100% success. it seems most live with a wonky idle or slightly strange power curve or poor economy or something. It's a tinkerer's sort of job, not something for a brand new car. The best advice for performance is keep the weight down.
Hope this gives you some food for thought.
Steve