NO wheel is perfectly balanced when made. Most are pretty close. The balance weights allow you to make it better. The weight system is simple and easy to make. The arbor is the difficult part to make but not bad for for someone with threading experience. The balance weights are three small movable weights on the rear or front of the arbor and provide static balancing much like a car wheel.
As for the bearings, there is no downside to "over engineering" them. We want to use bearings that are easily obtainable and reasonable cost as maybe others will want to build this project once they see it can be done reasonably. The bearing use design needs to be decided. Whether we use angular contact or taper roller bearings, they must be installed correctly. The Broadley spindle system uses Bellville washers stacked to provide preload to of around 10 pounds to the bearings and keeps the preload constant as heat goes up by allowing for expansion. the other method is precision ground spacer between bearings to provide the correct preload. this method is less forgiving in building because the spacer must be very accurate. Just a few thousandths too long and everything will get hot and probably ruin the bearings. A few thousandths too short and the bearings will be too loose which will affect the grinding finish. I have built both kinds of spindles and I know which one I prefer, but I would like to hear from the rest of you on this.
Also, what does everyone think about how many bearings. single bearing in each end, matched pair in the wheel end and single bearing in the rear, matched pair in both ends? my thought is single bearing in each end. It is easier and this spindle is fairly short so pairs will probably be too close together.
This is your chance to express your opinion and help decide on all the critical pieces of making a fairly large project, so lets hear some opinions.
....I say we can make the arbor and the balance system.
