First thing I would do is change your order of engineering. You’ll have better results doing this:
Listing trucks first is a bad sign, imho. It probably means you are putting weight on the truck choice, when getting other things straightened out first would probably have a higher chance of working well on the first try.
No, you shouldn’t even buy a washer from that site. It’s garbage.
This is also mostly garbage.
To me, this means you should probably scrap your whole list and figure this out first. I know it’s not welcome advice, but I’m not trying to make you happy with my response, I’m trying to make sure your first try at a build succeeds and I’m telling you what I wish I had been told. 
Engineering a custom electric vehicle is not like putting together a set of legos.
Tell us why you mentioned you’re not looking for a big board. Also not to be intrusive, but whether you’re 75kg or 125kg matters as well.
The battery is the most important part of the vehicle, and the part you should be spending the most money on. Nothing happens without the battery. Cheap out on other stuff if you want, but get a good battery.
Due to new laws in the UK, it might be hard to find small companies that will ship to you if your order total is under £135. Strongly consider looking at UK companies and if you need to import things, group them into >£135 orders.