You could get a tune for performance and probably leave it at that unless you really want an exhaust upgrade. You can always do just mufflers too if you want a better looking exhaust.
If you put a nice exhaust on it you should be fine with resale. Enormous cannons would probably cause you a problem, although you could just replace them before selling if you want to. Changing mufflers is a 15 minute job.
Wheels don't really matter because you can take them off when you sell it. Either keep the stock wheels or if you don't have space buy some stock wheels second hand when you want to sell it. However, putting bigger rims with lower profile tyres can quickly lead to the want for lowering. It's a slippery slope
Sway bars are a good handling mod that aren't too expensive.
Heavy duty rear sway bar mount is also recommended (is this still the case with Gen 5?), however you don't need to worry about endlinks.
Again, you can replace them if you sell. Or you can just not mention them and the buyer wouldn't know. Or you tell them they are there and the handling is better for it.
You can do lower spring or coilovers if you want lower. Depending on what you end up with you can also get decent handling gains here too.
If you have a manual you could make the shift nicer with an upgrade of shifter or gearbox/engine mounts. Slight NVH increase with upgraded mounts.
Plus whatever takes your fancy in terms of looks. You can get spoilers, lips, grilles, diffusers, eyelids, light globes etc.
In the end you can return pretty much anything back to stock for selling if you want, and unless you are doing something stupid you won't decrease the value of the car. You won't increase it though either, unless you spend a lot of cash, in which case you will be increasing the value of the car by less than what you spend.