Hi there. I’m hardly an expert as to this particular format, but I’ve done story stuff for a while, and I’ve got some input.
The thing with this particular format, I’m finding, is that you don’t really need MAIN qualities, and it can help to distill. When one thinks of superheroes, the mind is immediately drawn to the awesome powers and cool feats they can do - huck lightning, lift cars, read minds, fly around - rather than the recordkeeping of what their strength or intelligence score is. So I’d suggest distilling the "main qualities" into that, their powers and the levels therein, perhaps giving the heroes one or two major powers to start with (like energy blasts, telepathy, super-strength, shapeshifting…), with some minor powers acquireable through story means, like training or mad genetic experiments later on. You can even have them branch off the main power - a hero starts their life being able to shoot fire out their hands, for example, and might eventually refine it into rocket-assisted flight. I’d say: define what they can do, and define their personality a bit, without getting too crunchy about how many points of dexterity they have.
I like the idea of having a central "hub" area with branching areas quite a lot, actually, and think that can be your main strength as a design idea. One thing I don’t see a lot on SN is a mission-based quest system - you tend to start with a vague goal, and then follow stories until that goal sort of appears in front of you. If you have a dedicated mission-based system, where you do your hero thing in small side-areas or linear mission quest chains with a quick and definite beginning and end, I think it would really suit your subject matter. When you’re in the hub city, you could have it that the hero spends most of their time gathering reputation with various factions and doing the publicity work of being a hero - ribbon-cutting ceremonies, officiating weddings, visiting kids in hospitals, liasing with government bodies, performing super-science - with one-time or repeatable missions becoming available when they either trust you enough, you do a specific thing for them, or your do-goodery bothers a villain too much. You don’t want your heroes to be spending time mucking about in the slums, fighting random guys. You want them to be infiltrating the subterranean lair of the Night Empire, foiling their plans to collapse the city into a giant sinkhole.
Your theme is workable, and touches on one of the neater things about superhero stories that so rarely gets addressed: being human while also being a superhero. What do you do about, say, collateral damage? The Make-a-Wish Foundation? Weird superfans who don’t stop texting you? Do you even try to have anything like a normal life, or given the power you have, would it be selfish to do anything but save people at all hours, every day?
Think of how you want this to end. Do you want two major endings? Three? One? Fifty? Do you want to have options for your players to fail along the way, perhaps to the extent of needing to restart? What is the end-goal of being a superhero? Does the hero themself define it, or does the people they strive against?
Remember: The more complex this project is, the more difficult it’s going to be to execute, and the more opportunities you’ll have to bug something up. Pare down where you can. Minimalism is not the enemy.
One thing you’ve got going for you - you have an excuse to create scads of really cool villains. Steal my name! I want to be a memory-stealing psychic monster who gains intelligence by sucking peoples’ entire personalities out and leaving them as empty husks!