The newbiest question...

no, 60fps are fine. 120fps is pretty much overkill.

There is twixtor, but it sucks.

you cant boost fps, you have to use a software such as the twixtor plug in or after effects, to make an effect that appears as if a video was shot with super high frame rates. 60fps slowed down 50% to 30fps is more than enough.

shoot the 60fps and then conform it to 24fps or 30fps depending on what frame rate you want your edit to be. Then iif you would like it slowed down even further you can slow down the conformed clip in final cut.

I know everyone here seems to hate twixtor/ae pixel motion but if you're not overdoing it it really doesn't look bad. On some tripod shots that I've had of longboarding I was able to slow it down to 5000% length (yes ae does weird slow motion, I think that's 1/500th or something crazy. I can normally only get it to like 500% on normal shots) without major artifacting. For skiing, say you conform the 60p to 24p, you can usually get more frames from twixtor/pixel motion. As long as you watch and make sure you don't get the shitty artifacting it works fine.

false

Shoot at 60fps and make sure your shutter speed is at least 1/120th of a second. Any slower than that and your shots are going to look super echo'd and the motion will be blurry beyond belief - which looks stupid and Un-pro.

Try it out. If the shots at like 1/60th shutter speed then yeah, its going to look terrible, but as long as its shot at a decently fast shutter and it isnt completely overdone (like 90% of twixtor edits on youtube, titled gopro hd 400000000fps twixtor), it can actually work well. I know as a whole its not very good but in certain situations it can work pretty well.