bearing seals will depend on racing condition. if its outdoors, you will want to run rubber sealed bearings and indoors would be metal or fiber. though ive found it very difficult to clean metal sealed bearings with any certainty. what ive done with my stock bearings is remove one of the rubber seals from each wheel bearing, the seal seated on the cage and have those side facing together inside the upright.
my avids have a metal shield and rubber shield so indoors ill take the rubber seals out and point the open sides in toward each other.
this doesnt help for dif bearings really but its a start. good quality rubber seals are actually quite good just be careful not to bend the crap out of them when pulling apart to clean.
xray bearings are very good for stock bearings as are serpent though you need to properly clean and lube any steel bearings upon first use before they have a chance to gum up and grind.
low friction belts are definitely not just for show, as are hard coated pullies. though any non carbon plastic pullies work quite well. nylon or ptfe the like.
you can spend quite a lot of time building a car to make it right. I spend quite a lot of time building the bulkheads and drive train, ensuring they are as straight as possible. you can tell right away if any tweak is present when you tighten the screws which is why its very important to very loostly install all the screws and tighten them down in sequence, giving each part a little wiggle before tighting more.
I dont claim to know it all by any means. im a noob of 3 years but my serpent is freer than a lot of much more experienced drivers ive met