Thanks for all the quick and great responses!

Since I was half asleep when I posted last night, I might have misled on some points.
But, first off, you've
ALL reinforced my belief re always prime before painting as well as prime over repaired areas as well.
Sester: Thanks for the kudos on Sherwin Williams. Never used it so clueless on that before. My house is 20+ and it
was painted - but only once and that was by original contractor who built the house. We've never had the house painted since. Not doing kitchen cause we just had that redone last year and we redid our bathrooms ourselves. So only foyer, hallway, living room and connecting dining room & 2 bedrooms are what's in need of repair/paint job now.
Major settling and shifting in our basic sandy soil over all these years is cause of stress cracks. Plus admittedly bad do-it-yourself repairs on my part.

Additionally, we're "blessed" with truss uplift problem. That's the cause of most other seam cracks. (But that's another issue entirely, which we're dealing with another way.

Long story again). Remaining dings, holes, etc. are just from accidents, kids, cabinets/mirror replacements, pictures removed and ...Life. It all mounts up.
Chris: You said:
"Proper patching, prime everything and paint whatever sheen". Ditto. Makes me feel reprieve for using satin or eggshell if that's what I really want. As you said, too, it all starts from the bottom up. If 'foundation work' sucks, anything afterward will too.
ccarlisle: Truer words never spoken. Amen! Can't say how many times I've heard "
Well, I've been in the business XX years" as if that's supposed to impress me,
assure me they know what they're doing and that's enough for me to give them the job. Like you said, if that's their "currency" then their bank accounts contain way more monopoly money than real cash.
Matthew1970: Really appreciate your hint re circling those 'flat looking' areas w/pencil after priming is done.

Right now I'm looking at the small wall I did before that I mentioned in my first post and, yep, you can see those areas when you sight them from side. Dead on - you can sure feel them but you can't see them unless the light hits them jest right. Marking them - after first prime - would definitely make it easier to know where they are & re-prime them before final painting of two coats top. Agreed, too, that's why flat's most always used on ceilings cause you're almost constantly looking at it from an angle.
Thanks to your all your input and some basic intuition, I think my next move is to call a couple/few more painters. Knowledge is power they say. Reinforced knowledge - like you all provided - is SUPERPOWER.
Just one more

question re using stainkiller like a Kilz, Bin,etc. as primer for ceiling where trusses have left 'bleed' darkish lines across ceiling: We've used it before in bathroom that had stained ceiling as well as when we did the kitchen. But if it's used for purposes of trying to hide those truss bleed marks as much as possible, I assume it should be used for the rest of the ceilings where marks aren't as prominent. No? Yes? Would regular primer be okay then for just walls or should we just "Stain-Kill" the whole blasted thing (ceilings & walls) simply because nothing was ever repainted after initial contractor paint and/or because of all the sheetrock repairs that are necessary? Otherwise, I'd be okay w/using 'stainkiller' just for ceiling and regular primer for walls. Whatever?
Thanks again.
jay