What I do is goto Configure Controls and assign the keys you want to the secondary buttons. Simple, and effective - eg I have F1=Z, F2=X, F3=A, F4=S etc... When you've done that open up your skill speed bar and then mouseover the skill you want as skill 1 then press Z (if you use my steup).
Afaik you can't put teleport on Lclick, but yes you can have Tome of TP on hotkey like I said above
You cannot use skills just by pressing a key. You can only assign them to your left or right mouse button by pressing it. That means if you want to cast fireball and it's not on your left or right button, press the key to get it to there and then you can cast it with the mouse button in question as often as you like.
I saw it in a guide saying how someone had a key set up that you could teleport with the let mouse button and just press a key you had town portal bound to and it would cast it.
You can put Townportals in your belt and click the belt slot shortcut to use it.
As for other skills, I can see someone creating macros with complicated mice to have one click switch skills(ex: F3) and cast the skill(ex: right-click), but most skills in the game need to be aimed with the mouse.
You can not legitimately have teleport on your left mouse button.