Congratulations on being set on your path. Here are a few thoughts on your questions.
1. Yes, absolutely work out as much as you can before surgery, even if it means needing to take more Tylenol to get through it. It is not just so your muscles will be in better shape to get you through the process (which will be more critical as a short spaced bilateral), but my own experience shows that it can make a difference in your bone density, which will determine how fast or slow a rehab course Dr Gross will put you on.
2. As far as buying stuff; Dr Gross will have many things available for sale out of his office if you want to go that route; crutches, hip kit, polar care ice machine. They will have a walker available when you are in the hospital, though you would need to ask some other bilats if you would want one at home, which to me would seem like a good idea. For one thing, if you put a basket on it, you will be much more self sufficient about being able to carry things around the house. A raised toilet seat for your home is a must. Slip on shoes since you will not be touching any shoe laces for at least six weeks.
3. Help at home is very personal. I really appreciated help for the first week, it was a nice to have for the second week, and after that you can probably make due with some good planning before your wife heads out for the day.
4. I take my hat off to you guys that do both hips within the same week. I have had both of mine done by Dr Gross, ten years apart, and neither time can I imagine surviving both in one week. There are many people on this site that have done it, so it was clearly possible for them, but I would suggest having a heart to heart talk with yourself to make sure that you are up for it. You do have youth on your side, which is no small thing. For my own wimpy self, three weeks would be doable, two weeks would be challenging, and one week would present me with more obstacles than I can picture dealing with. I am certainly not suggesting changing your plans, since Dr Gross has gotten lots of people through your schedule, so he can give you realistic expectations. I would just suggest messaging some other bilats to see what they can share with you about the process, and then decide what you are comfortable tackling. My belief is that resurfacing is a much more challenging recovery for the first couple of weeks than total hips, but very worth it in the long run.
You are in the best of hands, and Dr Gross fully expects these to last a lifetime, so I think you have a lot to look forward to in the long run.