I agree with fishers; I'd want to see something more like the Yesterday Quest Toa which had Gelu in it too, but expanded to far more species. (Kinda like we do in the Multiverse. ) But the elements I'd want would be any that we haven't seen in action much really.
As for masks, I actually think I'd want mostly completely new powers. I always feel, when I look through the existing Kanohi list, even with my own additions like Conjuring, that there's something missing. Several things. There aren't enough that I feel are similar in the style of what they do to the original Mata masks.
There's a few, like Flight, but it feels like after 2006 we stopped getting much of the more basic powers and most of the new ones went off into stranger concepts like Possibilities. I like having those rarely but I'd want the majority to be more average, as that's most realistic.
Anywho, if we're limited to existing canon masks I'd want some of those original normal ones again, methinks. I don't really have specific preferences, any would do.
As for who would be the Toa, I'd like to see people who were once members of teams we know of that were disbanded if possible. I've kind of had enough of Matoran we're familiar with turning into Toa, frankly.