How far in advance planning for ski trip

All I can say is, good luck this year (covid).

I'd think most people plan 9-12 months out.

I'm currently planning to ski Tahoe in February, but on a normal year, I'd imagine most of the popular hotels would already be booked this close to winter.

You absolutely do not need to book a year in advance. We go during mardi gras every year and book a spot a few months in advance on Airbnb or Vrbo. Normally we are not ski in/ski out because we don't mind driving a few minutes to save some money and have a larger space.

This year lift tickets will be done differently for a good bit of the resorts. Seems that epic pass members will have priority, but I don't think there should be that much of an issue getting lift tickets. Maybe I am being overly optimistic

It depends on the time of year and where you are going OP. If you are going over the winter break holiday time or spring break then yes, you likely need to book in advance if you are going to be picky about where you are staying and price.

January is slow for skiing and travel in general as many people travel over the winter holidays, skiing picks up for February and then gets very busy for spring break again.

By where you go I mean some places don't have great snow all season so they don't book up like crazy as people know it can be hit or miss. Other places like Jackson Hole, Alta, and Whistler tend to be more popular with further out reservations due to very reliable snow. Most truly hardcore skiers chase the powder for shorter stays.