Cool kit!

I think the rule of thumb is that if it does not say "alnico" it's ceramic. Ceramic magnets are cheaper than alnico, so they go into most cheap pickups. That said, they also go into some relatively high end pickups like Bill Lawrence and G&L MFD pups.

I don't know about Vanson...but there are some very decent P90 clones for not much money. I'd probably go with ones made in Korea rather than China for quality control purposes. Most (including Wilkinson, I think) are made by Artec.

I test everything before I put it in. Any wires are probably fine, but i always test them for continuity before putting them in. I also test pots at least to make sure they are showing close to the same values, and I prefer audio pots for both the volume and tone...Alphas or ALPS are decent quality and will fit your holes. CTS and Bourns are decent quality and more traditional, but will require enlarging the holes. I'd also upgrade the jack...Puretones are my new favorite after being introduced to them on this forum. Switchcraft are the more traditional high quality jack.

All that said, you can build the guitar with the stock electronics and then just replace anything that fails or that you don't like. You've chosen a kit where making those sorts of upgrades later will be quite easy ;-)