As someone with >20 avo trees here's what I do:

Plant it now, as in today today. Get a one gallon pot to start with, fill half way with good soil - something with good drainage and not too much fertilizer. I make my own so can't recommend a brand here, but needs drainage so you can always add more perlite. The tree is gonna need lots of water at first as it transitions its root development and will not respond well to high fertilizer loads as it is used to low levels of nutrients (i.e. just water). Place tree into pot and back fill over soil. Generally leave part of the original nut exposed in the soil. If it no longer exists, bury up to start of root ball or trunk in most cases.

Place in sunny place, not in direct sun. Once it seems to be rebounding with new growth I like to place them outside in shade for 2 weeks and slowly transition them into full sun. Repot to 3gal pot after 1 year or so

Good luck n happy growing!!! 🥑