I’d almost hate to venture a guess on this one because a lot of this stuff is intertwined.
Normally an erratic idle is caused by a faulty Idle Air Valve or one in which the circuits are clogged up, but a vacuum leak could do the same thing.
As to the other stuff faulty mounts could allow excessive movement of the engine which can stress the radiator fittings due to the pushing and pulling of the hoses.
If you have faulty mounts you should have some vibration at idle and excessive movement of the engine when it’s revved.
If the A/C system is low then this means a significant refrigerant leak if it takes anything more than a partial can to top off.
There’s a lot of possibilities and unknowns here and I hate to even get into all of them but in regards to the leaking radiator has there been any overheating involved in this? Overheating will affect A/C operation and could possibly cause an idle problem.