The tech stack is probably one of the last items that should be discussed. Communities do not die because of the tech stack they use, but because of problems at higher levels.
IMHO a good starting point would be to identify features/processes that will ensure your new community does not suffer from the same problems you have identified with couchsurfing.com.
I joined CS several years ago when travelling across the U.S. At that time CS was a bit more popular in the States, but HC had more users overall, especially in Europe.
HC website was terrible with ads everywhere. There was a great community there and it's not website experience that matters, but many HC-ers first started using both HC and CS, and then tended to use HC less and less often. Although I've heard from a few people that while HC website sucks they had better experience with guests from HC than from CS.
Then a group of volunteers tried to rewrite HC website, but they got conflicted with the owner and started BW (bewelcome.org). I don't know what's the state today.
1. I wanted to make sure I am not just throwing an idea in the wind
2. The problem with couchsurfing now is mainly the poor website experience. I know this does not depend on the tech stack, but it's good to keep this in mind
As "features", I think those of couchsurfing are OK to start. Later on I think few things could be added:
1. jobs on the style of WWOOF and Work Away
2. Reviews, itineraries. Like I have an entire kayak itinerary for 2 rivers and I could put it in there or like where you can rent a kayak for a long trip, etc.
3. Guides. Like free tour guides, city walks, etc.