I always used to put the tree up (and other decorations) eithe Xmas eve or the day before. In recent years I move that to the weekend before if Xmas eve was a weekday - though we have to buy the tree at least 10 days before Xmas to be sure of getting a decent one.
Interestingly a few years ago a discussion with a work colleague who didn’t mind working immediately after Xmas - in fact positively wanted to - and apparently took her tree down the day after Boxing day She said she always got bored with Christmas. I asked when she put her tree and decorations up: 1st December. No wonder she was bored with it!
We have an artificial tree that’s about 30 years old and still looks good, and buy a real tree when we’re home for tall or virtually all of the whole period from Xmas Eve through to 6th Jan, using the real tree in one room and artificial in another, otherwise the artificial is the main (and a diddy one in tge other room).
As for buying decorations, other than the tree that’s a rare thing as they last for decades - just occasionally get something when we’re in a shop and see something that catches the eye - could be anywhere. We had a bit of a restock about 5 years ago when we saw some nice stuff in a department store garden department sale just after Christmas, and now have a choice as to colour scheme, or multitudinous which I rather like. We changed all the lights to LED around the same time, though they are a bit dim compared to latest models, and blue/green are brighter than red/yellow, whereas I’d prefer a warmer effect (a small tree in another room gets the ice loo with blue and white LED lights). I may replace them some time when I see some at a good price.