Fruit fly is the real problem, not growing it
Guava grows almost too easily here. What stops people eating the fruit is the Caribbean fruit fly, which lays in ripening guava and turns the inside to mush. In Central Florida an unprotected guava crop is very often a total loss, and the tree looks perfectly healthy throughout.
Two things work. The first is picking early: harvest while the fruit is still firm and just beginning to turn from dark green to pale, and ripen it on the kitchen counter. Most of the damage happens in the last few days on the tree. The second is bagging, which sounds laborious and is not: a paper or organza bag tied over a fruit at golf ball size keeps the fly off it entirely, and twenty bags is twenty good guavas.
Clear dropped fruit, every time. A rotting guava on the ground is the next generation of flies.
Keep it short on purpose
A guava will reach fifteen feet and fruit all over the top of itself where you cannot reach. It also takes hard pruning better than almost any fruit tree we sell and fruits on new growth, so cutting it back does not cost you a crop the way it would on a peach.
Prune after a harvest, take it back to six or eight feet, and keep it there. Everything you can reach is fruit you will actually eat.
Cold
Guava is the least cold-hardy thing on this list apart from soursop. It takes a light frost with leaf burn and dies back hard somewhere around the high twenties. Mature trees usually resprout from the base; young ones often do not.
Which means the first two winters matter. Mulch heavily, cover young trees on a cold night, and if it is in a container, move it. A guava cut to the ground by a freeze and resprouting in April will still fruit that same autumn, which is some consolation.