Welcome back Leanne! 😁
I'm going to give you my answers to these questions, but I can't guarantee that they're correct 😂 only that I've done them before 😉
1. I hardly ever compensate for age unless I've shot a roll from the batch at box speed and it shows me that it needs to be overexposed 😉 I've shot film from the 80s at box speed and it's come out fine, and I've had to shoot poorly stored film from the mid 2000s at +2 or more to compensate. If much of your film was stored under the same conditions, shoot a roll, maybe bracket it, and go with what works best.
What I DON'T know, and am now very curious about, is how multiple freeze/thaw cycles affect film. I know from my days in chemistry and biology that there aren't many things that like to be frozen and thawed multiple times, thanks to water's very odd property of being least dense at -4oC, so I'd be interested in other people's experiences with multiply frozen/thawed film.
2. My personal preference is HC110. It's dirt cheap and lasts forever (well, nearly forever). But with Kodak in some questionable straights, Rodinal might be best. I get most of my chemicals from Freestyle Photo in California.
3. If Ilford stop is just acetic acid like other stop solutions, it will be perfectly fine until the next ice age. You can literally use vinegar 😁 Stop solution's only purpose is to acidify the pH of your dev solution to stop the developer from working.
Now let's let some more qualified people answer your questions! 😁