This is a pistol with a folding arm brace, not an SBR.

Yes you need one Joseph.

Yes, a form 1 covers Short Barrel Rifles.

Yes you will need the Form 4 application. A Form 1 conversion is where you "make" the firearm (at least, for NFA purposes) from a non-restricted weapon, which requires that you engrave the receiver as the manufacturer.
A Form 4 transfer is where the weapon is already on the NFA registry as an SBR because the original manufacturer (whose information is already engraved on the receiver) made and registered it as such. In this case, you are simply transferring it via the Form 4, and no further action is required. -- Whether you go the Form 1 route or the Form 4 route, you will still submit the necessary forms, along with fingerprints and Chief LEO signature (if an individual transfer) or a Trust (if transferring to a revocable living trust).
The wait will be much the same (plan on about four months), and that is simply the nature of the NFA process, no matter which way you go.
The difference is that once you have the approved Form 4 back, then you're done, and can take the weapon home. Period.

Form 1 is the, Application to Make and Register a Firearm, I think form 4 is the one for SBRs and yes you will need to do one