CTC Prusa ebay clone questions

Hello people.

New to 3d printing, not exactly new to CNC/engineering, treat accordingly

Recently bought so called "2017 Upgraded Full Quality High Precision Reprap Prusa i3 DIY 3d Printer", knowing its cheap and tweaking will be neccessary. But, being of some CNC/engineering persuasion gave it a shot and it works fine for the most part.
For the time being it behaves.

However....

1. Decided to reflash marlin (came with marlin1.0) and got stuck with some parts of unknown origin that need to be specified. Mostly thermistors/couples. No idea what type they are. How do i know ? how to test ?

1.b. How do i dump original GT2560 board fw and settings before i start messing about with new marlin ?

2. I suspect bed not heating properly. I have an IR thermometer, nothing fancy, but when bed set to 70c i only read on it 45-50ish. Incorrect callibration ?

3. Optic interruptor end stops ? Salvage from old inkjet printers. Can i use them ? How ? Is it worth it ?

4. Printed wades geared extruder for next upgrade, what kind of torque motor do i need for it ? I have several smaller (than drive motors) nema17 steppers pulled from old photocopiers. They are a bit flatter. Will it work ?

5. Fast X movement makes a lot of noise. I have replaced smooth rods (printer salvage), checked bearings, no idea whats rattling ? Moved by hand no rattle, quick movement - terrible. Motor itself is quiet and not overheating.

6. Extruder (mk8 clone) skips on infill usually, for some reason. Nozzle doesnt seem to be blocked.

I'm sure to have more questions, but for now, this... At the moment most concerned to get answers to 1 and 1b.

Thanks.

My kids love new daddys toy, btw

1.
you get told.
you take readings at known temperatures and make your own table
you replace with known device.
you just pick a device at random (1 or 5 for 95% of cases) and check its reading correctly with independent temperature probe.

1b. google avrdude, also make sure you dump the eeprom.

2, IR probes are bad, they can't handle reflective surfaces and are generally inaccurate. Get a thermocouple temperature probe

3, yes can be used, no don't, they are prone to false triggering when hit by stray light.

Hi Baron What software are you using to update the firmware.
Thanks
Adrian