1. Should I get a steel plate or aluminum plate to start or will I need one for cold and one for warm water? Go with a steel BP. It will handle 98% of your needs.
2. How about a Dive Rite Transpac with no plate? Will that baby work for me? Yes, it will work. But, why go with it? Nice unit. I have one I dive for sidemount doubles. I prefer BP for single tank recreational dives - simpler, easier to deal with. IF you are hiking 3 miles in full gear to get to a dive entrance, then maybe a padded BCD like the TransPac may be of value. Otherwise, ...
3. What size wing? I'm thinking 40lbs. but you guys know a lot more than me. 30 should be fine for a single tank. 40 is probably just as appropriate for single tank diving. Get the 40. You won't have problems just because it is bigger and you can be sure the lift is (more than) adequate. Personally, given your description I would go 30. But, either is fine.
4. Should I get weight on the STA/bands? I know why I should, so you don't need to explain. But I need to know for what combo of cold/warm water - steel/aluminum plate? With a SS plate, in the tropics, you probably won't need added weight, but you may. In that case just use a weight belt. With a drysuit, in salt water, you most likely will need weight. If you need more than you want to carry on you waist, consider weight pockets. They can be acquired later. I have some I use with a single tank - usually with an AL 80. They are great, but not essential.
4. I have an Atomic SS1 Titanium safe second on my BC and I'd like to use it on the BP/W. It's easy to move but can I put it on a wing? No comment.
1. The Halcyon Eclipse. 2. The DeepSeaSupply system. 3. The Dive Rite system. All good approaches. I really respect the service Tobin provides.
If you'd like to recommend a specific setup, please do so. That would help a lot. I dive a DR SS BP, and an OMS BP, and a 'homemade' SS BP, and an OMS AL BP. I have an Oxycheq 50lb wing I love, a Halcyon 55 lb wing I like, and a DR Recwing I use a lot. (All this is for doubles.) I use the DR SS BP for singles. Frankly, I am comfortable with a variety of rigs, and have trouble saying one is 'better' than another. I doubt you will be disappointed with any of the ones you are considering. Oh, have I mentioned that I really respect the service Tobin provides.