Welcome to the site and congrats on the purchase.
1. Play with the firewalll quadrant adjustment and see if that helps the clutch any. Also look to see if the clutch cable is adjustable( this will be at the
tranny, where the cable runs through the throwout fork, if there are threads you might be able to adjust it some to see if that helps) If not I suggest buying an adjustable one first and see if that helps ( steeda sells a great one) If you are still having issues, the it sounds liek the clutch to me.
2. When you drain the
tranny fluid take note what color it is. It should be a ruby red, a clean ruby red at that ( assuming he used the right fluid for the T5). If it is dirty looking then your
tranny may be on its way out. However if it is clean then you just narrowed down your gear issue to your clutch hopefully.
3. Idle is about 850-900. Mine idles at around 900-1000 depending on the air temp and how warm the engine is. You can try to clean the throttle body ( they do get nasty and this affects idle), rear end gears wont affect idle. Check to make sure the MAF sensor is clean and that the air filter is clean, Make sure that piping from the air box to the throttle body is tight and secure as well.
4. Motor takes 5 quarts of oil.
5. Does it squeak when you give it gas sitting still or in gear? Check the suspension, see if there are already poly bushings on it. If not I would recommend them. Also check to see if the
tranny mount is a poly mount ( usually red) if it is red congrats you have a energy suspension motor mount and the red ones are notorious for squeaking...you can try to apply grease or just ignore it.
I would also check to make sure the sway bar mounts aren't shot and try greasing them if you can. If you already have poly suspension mounts try applying a small amount of grease to them and see if that helps.
Hope this helps, let us know what you find out with your issues.
Drew