Welcome to CC.
Virtually all hotels have some standard early afternoon "official" check in time - that doesn't mean you can't check in earlier. Some charge to check in early and room availability will depend on what's going on that day. Virtually all will allow you to leave luggage (for a fee or free).
You are very unlikely to win a GS from an OV regardless of what you bid - most folks winning (for whatever they bid) are usually one or maybe two categories up from existing cabin. Never mind that winning anything is usually rare.
Again, the issue is not canceling, nor keeping the cabin, it’s canceling just one person and expecting a refund (including the cabin fare) for that person. If you try to cancel for COVID for a refund, it generally requires canceling the entire cabin/booking.
The issue is not exposure, but the possibility of only one person on a booking being able to cancel for COVID reasons (with a refund )- not usually possible.