Nope but it is useful, for example when you are using thrusters
E
Yes
well first you need to get hoverboard mod then once you have got that from garry's mod related files you get a skateboard pack and put both of them into addons
Yes
No. it is PC only.
To get in a seat/car in garrys mod you must press your use key next to it (default is E). If you do not know what your use key is go to options and check in keyboard.
gmod is for PC only
yes
yes
If you use steam, right MB on the picture in steam and then delete.
The default use key is E, but you can change or check what it is set as by going to Esc > Options > Controls.
Well, in the steams list of games which you can use on garrys mod it dosent show Half life Source. But if you type in gman squad on youtube you can see their playing the storyline on Half life Source. I asked them the same question and they said yes, you can play the storyline if you have garrys mod and Half Life Source. I dont know for sure because i have not yet tried it.