Sure if you are milling in the micron ball park. Anyway once you spindle reach thermal equilibrium you don't care anymore about this.
Fair point and and seems to be the mailn difficulty with building high speed precision spindles is getting the correct clearances at operating temp.

You did only mention axial expansion but the real problem (for a diy spindle) I think would be the radial expansion and the resulting change in bearing clearance

if its preloaded when cold it can cause brinelling problems if not used regularly and if the preload increases during the warm up period then there is the risk of overheating and to much preload binding and associated damage.

Therefore I think needle bearings would be difficult to use if mounted in the front. Btw Did you mean needle bearings or roller? as I dont think needle are suitable for high load and cant have a taper added to change the preload. Are they?

Do you have a diagram and design use for that spindle?