The starter prob sounds like a weak battery/poor connections/bad starter/bad starter bushing. Reverse popping out/second gear feeling "shorter" in the shifter may be shifter adjustment. May also be the trans going bad, that's usually what popping outta gear means. Bearings get loose, gears cock at an angle and slide across each other and out of mesh.
You said you changed the clutch a while ago? ALL this could be loose bolts. Check all bolts, wire connections and oil levels.