Registry advice

I think you should register for what you need or want, and not really go by headcount. Some registries allow you to mark some items as favorites so guests know which gifts you absolutely want to have. That way even if you have many many things you will likely get those items...

I kind of had this same issue just with less people. FH and I already live together but we had a bunch of random hand me downs and mismatched items. When I was looking into what to register for, I think they recommended registering for twice your amount of guests but I had a hard time finding that many gifts that I would be interested in. Depending on where you register, you can mark things as your favorites or even make an item a "group gift" allowing multiple people to gift it to you. If you find a lot of your gifts are more expensive, I recommend doing that. But as Ka-Rina said, register for what you need and want, don't aim for a certain number because then you might end up with gifts you don't want and you'll only end up with a store credit for them.

We invited 223 people (probably closer to 100 households, we have a lot of friends that are married with kids and we included all of them), and my shower had about 40 people. For the shower, I added more gifts about a month before all under $50, then deleted the unpurchased ones after the shower. I knew people didn't want to gift cash or spend a ton on shower gifts, it worked out great because almost everyone who came purchased the gifts I added. Our registry had around 90 gifts total, including the shower ones.