Installing Baseboard Moulding with Brad Nailer
If you are renovating the whole house, or at least a good portion of it, I would purchase a nail gun over renting it or borrowing it. Owning it lets you use it when you need it, not like going to get a rental and returning it or being responsible for somebody elses' property. Get the compressor too, it does more than power nailers, it fills tires, blows dust off things big time, inflates balls for sports, etc.

Size your nails so it goes into the framing about 1". More is overkill, but a bit more works if that is the size of nails you have on hand. No finish nail needs to go in the framing more than 1 1/2" In that depth, the possibility of hitting wires or pipes grow. Kick plates that protect pipes and wires per the building code are only needed on wires and pipes closer than 1 1/4" from the face of the stud. That's why 1" is the sweet spot, good holding power and less chance to hit stuff in the wall. Using a nail that is too short will increase the chance of the trim coming loose.

Add up all the thicknesses of the material you are going through. In the case of a 1X6 baseboard and 1/2" sheetrock that is 1 1/4" of material, in my opinion a 2" (6D) nail is too short, it will need 8D nails (2 1/2" for the holding power required. With that size of nail, you will need a 15 or 16 gauge finish nailer. To set nails in the trim to the edge of a door jamb, an 18 gauge finish nailer will work there. With the larger nails around the edges holding the trim to the drywall you can go with a slightly smaller nail to hold the trim to the door or window jamb. 1 1/2" long is what I use there. You could use 2" but the chance of blowing out through the face of the jamb is high.

Big box stores usually have a combo kit, a compressor with 2 nail guns, a good deal, in my opinion.