Alright, I'd say there's a decent amount of interest.
Plotline, I was thinking a return of some of the previous villains, working together in their own way. Myotismon, Lucemon, etc. As well as the return of the X-Virus/X-Antibody (From Digimon World 4 and the X-Evolution Movie) to add a little more to it and give more possibility.
As for series, well, we know Seasons 1-3 were all linked together. (01 and 02 was on TV for the Season 03 characters.) I never took much liking to Frontier and haven't yet got into Savers. (Played the PS2 game though.) Basically, it will be a collaberation of mostly just Adventures and Tamers, mainly because some people may have lost interest after Tamers, but still understand everything before.
We can all start out doing our own thing, and work together, or against each other. We can have Tamers working for the bad guys as well as Tamers working to fight against the bad guys.
If you want to use Biomerge, go ahead, though you don't have to. Common and Fusion are staying, as well as the Eggs, as I mentioned already.
I would suggest playing as both your Tamer and Digimon, unless you want to be a rogue digimon. Rogue digimon will be able to digivolve, when they absorb enough data. (As in Tamers)
There is no limit to characters, as long as you can keep track of all of them.