Planning on taking a Techslinger and later integrating the rifle with a cybernetic arm. Would integrating a small rifle be treated as a one-handed firearm?
Unfortunately a weapon being small does not change its 'handedness'. It is still considered a two-handed weapon. However if this is a home game, you can always ask the GM to allow it.
You can always integrate a Dragoon Pistol, if you're doing it for the range, I suppose. But, by raw, integrated weapons are a) considered Natural Attacks and b) generally limited to light or 1-handed weapons How are you GETTING the integration?