Bear in mind you can buy 3 or 4 year old trees from the nurseries. We are also coming into bare root season, when the trees are dormant, you can buy them without containers, this usually means they are cheaper. Worth having a look to see what your local nursery has on offer. You can talk to them about what you are after too.
Some tree fruit will need another suitable tree to polinate them, some are self polinating.
With things like Apples, you'll need to decide if you want cooking and/or dessert apples, ripening times, storage suitability etc.
Then you've got pests to consider. We put grease bands around the trunks to stop things crawling up the trunks.
In the UK a late frost can wipe out the crop by destroying the blossom, I take it you get less frosts where you are?
