Reverse is unsynchronized except for late 93's. That's when the t-5 finally got a synchroed reverse.
The teeth on the reverse engagement gear often round over with age. When they do, it makes it tough to get into Reverse. You might need to go into a forward gear first to stop and align the gears and try for R. If it doesn't go then, you need to let the clutch up in nuetral to spin the gears again and then stop them in a gear and try again.
Reverse parts are not replaced in a typical rebuild. The idler gear is about $40 and the 1-2/reverse slider is about $85.
As for 4th gear, if it's not a clutch/fluid issue, it sounds like the 4th gear blocker ring is wearing down. If you replace it now before it starts grinding, then you might get away with a $20 fix. If you start grinding 4th, the price could go up.
I think you had another post that said your t-5 was whining as well. Sounds to me like your trans needs some refreshing