Same as bpe, I've found the valve train to stabilize after the 3rd adjustment, so after about 20,000 miles or so. At that point, I can get 10,000 miles out of an adjustment, though I never push it farther than that, even though it's not uncommon to find all the valves to be within spec, albeit very close.
As for advice on doing the whole job, the best has already been given: take your time. Also, do it right or do it twice. Cutting a corner off one procedure will add two corners elsewhere.
I, personally, can do the whole job in 2 hours with a beer in one hand. If it is your first time (or even second or third), you'll need to budget WAY more time than that. It takes a lot of practice to know exactly where everything is, what tools to have on hand and to have the clearances memorized.
Lastly, if you think you did something wrong, you probably did. Double check your work. And for the love of god, make sure the two dowel pins in between the valve cover and head are accounted for. If you are putting the valve cover back on and can only find one dowel pin, find the other. The most likely place for it to fall is inside the engine and will render your valve adjustment moot in a hurry if you fire it up.
1990 EX500 - 142,000 miles as of August 12th, 2019
1993 Ducati 900SS - The real canyon carver