You don’t even need all of that really. A lot of Steam functionality can be utilized just by adding it as a Non-Steam Game. Steam Workshop isn’t the necessary if you have a modding scene, you just need a good mod manager.
The key point on whether I’ll use your storefront or not is whether your plan for success is to buy out anti-Steam contracts (remember that it’s not exclusivity to EGS, its to not release on Steam) to get customers and low revenue cuts to get developers and most importantly, to run a loss leading business for a number of years until you are profitable. If EGS were to ever become profitable, how long until they switch to squeezing out as much as they can? They’ve already rescinded their “curated” catalog.