If you buy the base 370Z, I would change the HU asap because the quality of that unit is really bad. Also note, with base unit, you do not need any dash kit. If you buy a touring 370Z, you need to spend $40 and get this dash kit
Metra 99-7607B dash kit for Nissan 370Z is NOW AVAILABLE!. Try to get a good installer to install your unit. The problem you're currently having (a/c not working, poor wire connections) is due to poor install. Just use your current pioneer if it's in good shape, no need to buy a new HU. Hope this helps.