Comfort is the biggest thing to look for. Sadly, you can't always predict that out of the package. I'd go for new shorts and shoes, because as you start riding longer, those seams and threads are going to get more annoying. Following that, a new jacket. I don't know much about riding off-road, but I've layered lined track pants over bike shorts and was toasty. If you're going to spend money on anything, spend it on shorts.

Foska, by the way, makes some fun stuff and is based in London. It's not cheap, but if you create an account, you get a bit of a discount.