what should I know before investing in a player home?

[Sylfaein]

In addition to what's been said, don't be too quick to buy things off the MB! Always google the item to see if it's sold by an NPC--quite a lot of decent housing items are, now. You can get them off the MB anyway, but you'll be paying a markup for the convenience. Go to the Independent Suttler NPC in the housing ward, and purchase a permit for a steward, as he has TONS of housing items to sell you. If you craft, be sure and pick up a material supplier permit, as well; there's actually a surprising number of nice furnishings you can craft from basic mats. I won't do a decorating job without a steward, a material supplier, and a summoning bell at hand.

[worldofneil]

Make sure you have the money to build a house on the plot as well, as you're given I think 2 weeks max to build a house on the land before it is relinquished automatically.

There's no specific demolition timer for plots without an estate hall, so the earliest it can demolish is 45 days still. It's literally just that without an estate hall it's impossible to go inside to stop the timer hence they get auto removed if not used.

[Gabriel_Hope]

There is a requirement for personal housing, you have to reach Second Lieutenant rank in your Grand Company.

[Zigabar]

Don't forget to have an Miniature Aetheryte on hand when you go to purchase! Then make sure it's the first thing you plop down. Without that, you can't teleport to your house. You can buy one with GC seals.