After getting my radiator situation straightened out, I am going to attempt to get all the tubing bent and fitted. My question is, if I get a tube bent and I find it needs some fine adjustment, am I able to apply heat to it again to get it where I want?
 
Since it is my first time doing this, I doubt I will get these bends exact first time and I feel that there shouldn't be any undue pressure on the O-rings or am I worrying about nothing? I have bought lots of extra tubing just in case  :D

You can reaheat it, but unless you leave the insert inside after the first heat/bend it will warp (at least in my experience) a little no matter how careful you are with the heat. I'd make sure you have extra tubing on hand just in case.