Fuel gauge and "idiot light" work off two different sensors. Check that there are no loose/broken wires first. Then you could try replacing the whole in-tank sender unit. There is a rubber access hole thing under the carpet in the hatch, keep digging until you get it out. Is an idea to drain the tank first.
On 4As oil pressure is fed off a single wire running from the sparkplug side of the block. Check this connection and trace it back.
Exhaust leak sounds like ticking, see if you can feel exhaust coming out round the manifold etc or take it to someone who knows the sound, they will be able to tell straight away. Or maybe your engine is just rooted.