For dry yeast, don't do a starter. Just pitch half the pack. If you want to rehydrate with water you can Preboil and cool to 85-90F then sprinkle half the pack into about 50-100 mL water, wait 15 mins shake it up and pitch.
Welcome. I got a 1 gal kit last year and have been hooked. I would get a 3 gal pot if you can. It makes life a lot easier and affords you more options as you try new things. I have a 3 gal and which has been perfect for 1 gal batches on the stovetop with extract, partial mash or BIAB. I don't...
Either way will work just fine. You can always add water at the fermetner or let it boil off a little longer if you have too much. If you know your boil off rate specific to your 1 gal brew setup that helps, but it sounds like you might need to do a few 1 gals to figure that rate out. If you...
I always do full volume boils with my 1 gal batches, even with extract, rather than adding a bunch of water to the primary. As far as the water volume for the steeping, it probably doesn't matter that much.