I like what Isopod did, linking them directly to a instance.
The only way to catch the average joe is to hold their hand and get them to content as quickly as possible. While linking them to the largest instances may not be the healthiest for decentralization, it's going to give newcomers the best experience.
A lot of redditors, I'd even say the majority now-a-days, use the app. While a lot of the Lemmy apps are great. I wish there was one that guided you through the entire signup process.
That's a small description of the basic functionality. It does not address things like in the OP (where do you "meet" - mostly an analogy going bad from being overextended), what's the point of different servers instead of a big one, etc.
I've been reading fxomt's FAQ (Blaze linked it a few comments below), I'm going to do something like that.