Hey, welcome to AFN, and congrats on the impending retirement. There are no dumb questions here, you will find this forum one of if not the most friendly and helpful ones you find anywhere.
Before I comment on your specific question, you might want to consider some additional thoughts from another retiree new to the growing game after decades of not using weed. It sounds to me like you are going to find the new stuff a fair bit stronger than what you used to buy. Current strains are stronger, and regardless of that, buds alone are lots stronger than a mix of leaves and seeds. So as the saying goes, start slow and see how the new stuff works for you.
Also, I suggest paying little attention to THC levels in choosing your strains, all of the strains you are likely to grow will be plenty strong enough compared to what you remember as long as you are not choosing dedicated CBD strains. I suggest just thinking about the effects you prefer, and dig around to see what other growers have to say about different strains. Same strain name from a different breeder doesn't guarantee same results though, so keep that in mind.
As to your question about trim, if you are growing only for yourself and are not a heavy user, even a small grow like the 2x4 one that I started with will give you more really nice bud than you are likely to use in quite a while, at least it will if you dig up and follow the advice available here and elsewhere on how to grow. If your grow goes even moderately well, you will not have to smoke or vape trim. Do yourself a favor and plan on just using the bud after a clean trim and nice cure. I highly recommend getting a decent vape rather than smoking the stuff, it will taste better last longer, and likely treat your lungs better. In fact, the flavour of nicely cured bud from a good convective vape may be a whole new level of enjoyment for you if all you had in the past was schwag smoked in joints.
By all means keep the trim, but you are unlikely to need it, especially if you end up having fun growing - your second grow will start a long time before you run out of nice bud. If you decide later to try some sort of extraction, the stuff keeps reasonably well, especially if you pack it in sealed mason jars and freeze it. However, same as for frozen bud, let the mason jar of goodies completely come to room temperature before opening it - doing otherwise risks the contents getting moist due to condensation. Even if it turns out that you decide not to use the trim yourself, you might know someone who would like to use it for extraction. In any case, you will probably have enough really nice bud to keep you well supplied, and enough to share with interested friends, so plan on trimming well, making the effort to do a good cure, and keep that trim separate.
One final suggestion before stopping my blather. I strongly recommend that you try to keep your first grow simple. All you need for nutrients is few of the Megacrop products. Don't spend a pile of money on other stuff that claims to be fancier or more effective - Megacrop works extremely well, is easy to use, and it's cheap, especially if you get in on the sample offer that has been available recently. The sample will do your entire first grow easily unless you start bigger than a 2x4. Just order the basic nute mix, some Cal Mag, and if you are inclined, some Sweet Candy and Bud Explosion, although I suggest that for a first grow the last two are optional.
Good luck on your new retirement adventure. Take my retired word for it, growing weed can be a lot of fun quite aside from how much bud you generate. And learning new stuff is good for us old buggers.