Hi,
I was a Tau player who started High Elves, too
Units/models that you should not bother buying as far as rules go are:
-Silver Helms
-Excess archers
-Excess spearmen
Obviously you need some archers to meet your troop requirement, and possibly a block of spearmen. But no more! Your strengths lie in the elite units of the army.
All of the elite units are excellent
imo. I would look through them and see what you like to make an army theme. I personally don't like it when an army has one of each... a unit of white lions, swordmasters, and phoenix guard. It's more fun to focus on a few to have a strong theme.
Swordmasters and Dragon Princes are awesome! White Lions would be cool if you're considering getting a lion chariot; Phoenix Guard are a good option but more to hold fast than do anything else.
But just make sure you get a theme and go with it! The models are expensive so you don't want to get any that aren't leading you towards your goal of a fun, cohesive army
You'll also want to make sure to include a few bolt throwers; you'll be forced to take two small units of archers for core requirements, so you might as well have some real firepower to go with them. The rest is up to you,
imo