Survive mostly. Create Block is ultimately the key to stopping rushdown I believe. I don't have a winning formula on hand, but even just jumping and putting a block under you slows down your opponent enough to chain a block path away from them. From there you can decide if you want to jump down or create a second block path above/below you or utilize the stage platforms to make your escape. Add in TNT or the anvil here and there and you can sufficiently confuse your opponent.
You of course need a solid understanding of spacing and your opponent's character as well as the execution to pull of these block creations quickly while still keeping a general sense of what's going on. And I think that this is where the learning curve for Steve is going to get really steep. But Create Block can shutdown rushdown characters that don't have significant disjoints pretty effectively. And then diamond weapons can pretty quickly make up any lost ground.
But you're probably SOL with characters that have large disjoints like
![Zero Suit Samus :ultzss: :ultzss:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
![Marth :ultmarth: :ultmarth:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
![Lucina :ultlucina: :ultlucina:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
or have strong projectiles like
![Zelda :ultzelda: :ultzelda:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
![King K. Rool :ultkrool: :ultkrool:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
![Richter Belmont :ultrichter: :ultrichter:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
![Simon Belmont :ultsimon: :ultsimon:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
or certain playstyles like
![Snake :ultsnake: :ultsnake:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
![Min Min :ultminmin :ultminmin](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
. You would need to have some really fancy movement to deal with the disjoints and really good spacing and shield game to dealt with the projectiles; all of which aren't easy to do consistently online.
As far as finding time to mine goes I find that eschewing juggles and edgeguards in favor of getting resources seems to be the best option. Steve doesn't have much in the way of approach tools, so mining whenever the opponent is at a safe distance seems to be the best bet. I don't think you will need to worry so much about iron so long as you keep a healthy supply of block resources.
I think this character is going to have a really weird MU spread in general. He can shutdown characters like
![Sonic :ultsonic: :ultsonic:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
![Pichu :ultpichu: :ultpichu:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
![Pikachu :ultpikachu: :ultpikachu:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
well enough with clever block placement, but then seemingly gets bodied by the likes of
![King K. Rool :ultkrool: :ultkrool:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
. I think projectile zoners and those who can out camp him are what his actual archetype struggles are.