If all you have is a tub, then it's highly doubtful that the walls adjacent to the tub are waterproof enough to be able to add a shower without causing water damage to your home. (Even if they are covered with decorative tile, they're it's probaly installed just over drywall.) I'd be a much better idea to plan on renovating the bath completely before you move in. Or, only take tub baths until you can renovate.

Make sure that the glass is meticulously clean and for best results use an adhesion promoter on the glass and SDL muntin bar as well before applying the tape. Attach the VHB tape to the muntin bar, leaving the paper on the other side. Pull about an inch or so of paper off the tape to the side, but don't tear it. Carefully lay the muntin bar on the glass allowing the exposed tape to adhere to the glass. Then slowly pull (to the side) the remaining paper from the tape as you press the exposed tape to the glass. You won't have full adhesion immediately, and you can remove the tape from either surface at this point, but better if you don't have to. No caulk or other materials/adhesives are needed. VHB is amazing stuff. I have been involved with glass ceilings that were attached using VHB tape to hold the brackets that were used to attach the HEAVY glass panels in place.

I'd take those USDA garden zones with a big grain of salt. Those garden zones specify simply how cold it gets in the winter. That may or may not be pertinent to decisions about date of last frost. To wit, I'm in USDA zone 8a - central Texas, and my tomatoes are out in the ground. But spring gardening is quite different in Seattle (I used to live in the PNW). One would like to believe an app would be able to do it right. When I look it up, I see that Seattle frost "safe dates" are mid-April. So I agree that it's a month-ish early to be seeding frost-intolerant plants. If the seedlings are kept cool, like the 60F you're seeing, they'll grow slowly, however, and you might be able to start them soon.

What do you mean by "flushes properly'? And are you adding the dish detergent to the tank or to the bowl? Sometimes adding dish detergent to the bowl can help break up a clog. Do you have a clogged toilet?