HELP! NEW and need advice about 1997 MAXIMA GXE!!

[ILLmaxima]

Hi. I just bought a 1997 Nissan Maxima GXE. It has a VQ30DE engine in it with automatic transmission. It is in AMAZING shape, well taken care of, and extremely clean. It has 146,000 miles on it and i bought it for $5,100.00. I have a couple questions..

1) How much would it cost to swap out the AT Transmission with a MT?2) Are there any more powerful engines that I could swap out to make more than 190hp? Like a Silvia or other engine that would fit and make it more powerful? Also how much would one of these engines cost?3) If I bought a Cold Air Intake or Short Ram Intake how much of a power increase could i expect to see in terms of HP and Torque?4) Are there any dependable Turbo Kits that would work for my car and what else would i need to make sure i don't blow the engine (EMS, CPU, whatever ANYTHING else id need) ? How much would one run me?5) Would it be practical to do either one of these considering i bought the car for $5,100.00 ?