Did you get your fuel tank to read correctly yet?
My '89 had sat for years with the sender sitting at a half tank so it would read wonky when it hit that spot. When I took it apart the sending unit had corroded and crumbled.
I repaired it for a few dollars with parts from a junkyard, non corvette GM parts.
This is what it looks like when you get into the tank:
The whole hanger is held in with bolts and there is a rubber gasket. Unplug and unbolt and you can pull the whole assembly.
When I did this repair I was able to reuse the rubber gasket, have a plan in place if it is not usable.
As for the sending unit, it is the same one used on GM's of the vintage. If you look at the picture for the corvette hanger attached to the float (black cylinder in picture) there is a "D" shaped gold colored canister, this is the sending unit resistor and sweep. Get a new or new used one from a GM and swap it in. As my C4 was an '89 I grabbed a sending unit from an '89 something in the junkyard and its resistance measured identical to my broken one, but it wasn't broken. (I think I used a full size caprice or something)
Check out this picture, I'm pretty sure GM kept the same sending unit resistor for years:
What you can see in this picture is the wire is riveted on, you can drill out this rivet and use a nut and bolt. On the opposite side of the stamped steel "D" shaped cylinder are a few tabs bent over to hold the assembly together, bend those out to access the resistor and sweep, either clean your existing assembly or replace with a good unit.
See here:
and here:
As for your hard brake pedal, this is a common C4 problem when they are daily driven gently. You most likely have a glaze built up on the pads, before you replace them try to remove it with a few back to back high speed stops. This brought mine back to life.
Enjoy the car, I miss my C4.