You really dont want to put latex over plastidip because it will peel off, where as when latex is brushed over foam, it bleeds into the pours and wont come apart. You can plastidip it all black at the end, before you dry brush the silver but I would strongly suggest only dong that at the end. I guess simply put, you really cant cheat the process ...but the process is rather straight forward. With your build experience already, I'm sure you could do this suit on your own in a heartbeat.
No, latex does not come in a spray can, that's why I have to use a spray gun with it. It's liqud rubber...comes in jars or pales only.