Currently screwing/gluing down a new plywood under floor in my kitchen. Now ready to nail down solid oak hardwood slat floor. I am looking to buy a nail gun as some are cheaper to buy than rent. This will be for the wood near walls, I already have the large nail gun for the majority of the floor work.
Questions:-

1 Any difference between a nail gun and finish nail gun?

2. Which gauge will I need to nail down 3/4" solid oak slats into plywood?

3. These are the three guns I am currently looking at. All I can find at reasonable prices.

WEN 61720 3/4-Inch to 2-Inch 18-Gauge Brad Nailer

WEN 61750 3/4-Inch to 2-1/2-Inch 16 Gauge Finish Nailer

Hitachi NT50AE2 18-Gauge 5/8-Inch to 2-Inch Brad Nailer

4. Any particular length for the nails?

Thank you

For trim out flooring I would use a 16 gauge, 1 1/2". 18 may be too small to penetrate 3/4" oak flooring. Typically, I use 16 =75%, 18= 20% and 24=5%.