Cheap 1/4 drive with adapter will work just fine.
What kind of marks? It'll probably be fine.
It'll work to pull the old bearings off, but if you want them off undamaged you'll want something more like this. I will say after rebuilding my axles, unless you're planning on rebuilding more in the future, or are really interested in learning how to do it, it is WAY easier to just pay someone else to do it.
Oil leak can be a lot of things. Could be valve cover gasket, could be oil filter adapter, could be rear main seal. Just gotta look. To clean the engine, you can get a spray can of engine degreaser. Follow the instructions, you'll have to warm up the engine.
Steering box replacement isn't too bad. There's a lot of debate as to whether or not the durango box is actually an upgrade, but if it is an upgrade, it isn't much of one. It is bolt-in though, no difference between the two. Just get a stock replacement.
The tick is probably the purge solenoid. Could also be a lifter but if its intermittent it's the purge solenoid.
Junkyard will probably be your best bet for the tensioner bolt.
Wind noise is probably as good as it's going to get. You can try and use a sound-deadening product like Noico or Dynamat on the tub.
You can get a mechanical gauge that fits into the same hole as the pressure sending unit, but if you've been driving it for months, it's definitely the sending unit. A new sending unit is only $20-30.
Repairing a bent frame is generally beyond what a garage mechanic can do.