I don't know about Portugal, but in Brazil we'd NEVER say "Manteria uma distância", unless it was something like "I'd keep a safe distance from the car ahead of us" (Manteria uma distância segura do carro a nossa frente).
Just like it is here, it'd never be used. We'd say "I would keep my distance) - "Me manteria distante" (grammatically wrong but commonly used) or "Manteria minha distância" (literal proper translation) C:
I think it would be irei a usar if I have a good grasp of PT Portuguese.
Usarei / Vou usar
(Irei usar is informal, more than "vou usar").
It's redundant, you know? Using the future form of a verb in an expression where the present form already expresses the future.
But curiously, despite what grammaticians might say, people tend to think that "irei" is more formal than "vou", and they have adopted this.
If you really want to go formal, pick "usarei", if not, just say it as everyone does: "vou usar".
"Irei a usar" sounds to me like something they'd say in Portugal, but I can't confirm that xD
Here in Brazil we would use "irei usar" (or "usarei"). If you're having a conversation you can also say "vou usar", but this one is frowned upon when writing!
HAhahah! Thank you emeyr! C=