I don't profess to know if it's a good idea or not, but here are some considerations, assuming you mean for the Steam version to be a paid game...
Steam's advantage as a platform is that it has huge reach. Steam's disadvantage is that they take a large cut of your revenue. It would make more sense to me to have the free version on Steam to leverage the reach and the paid version outside to collect the cash.
Developing two versions of a game is additional work and possible bugs/maintenance. Especially when it might not be necessary to have two different versions at all. Why not use the same business model for both?
People can react extremely negatively to pay up front games that act like freemium games in disguise (SW: Battlefront 2). They can also react badly to freemium games that hit users with a huge wall to progress locked behind IAP, essentially becoming pay to win. It sounds to me like your approach is to do both. There can be a good balance in the middle somewhere, but then you would only need that one balanced system and not two separate versions.
All my personal opinion - I have no experience publishing games.