in order asked.
1 should be fine, the new motherboard will just have more ports, features, and options.
2 the motherboard is the backbone of the system in that everything is connected to it, I suggest watching several youtube videos to familiarize yourself with the process beforehand, but if you can turn a screwdriver and disconnect cables you can do it. 👍 I will post some detailed grounding instruction for computer assembly at the end of this post.
3 the power supply is the food source, out of spec or bad power is akin to eating lard and sugar only. its not healthy and damage will be done. Cooler master PSU's are known for their mediocrity. They only sell a few good ones and the lite is not one of them.
4 I just upgraded to the 1500x a few months ago, before that was my trusty 955 black from 2009. for me your CPU is an upgrade. it really depends on your needs. do you need more power? the CPU and the GPU look well balanced to me.
Assembly grounding:
plug in the power supply to the wall. you can touch an unpainted part of the PSU (insert an unpainted unfinished screw into the PSU mounting holes and touch the screw as a grounding point) once you have grounded yourself you can now touch and assemble the parts of the PC.
if you move your feet, or shuffle in your chair, reground yourself again.
install the CPU into the motherboard and the RAM into the slots.
if you move your feet, or shuffle in your chair, reground yourself again.
install the cooler to the CPU. install the motherboard into the case.
secure the motherboard down with the screws, make sure you remove any unwanted/needed mounts before securing the motherboard.
unplug the PSU and ground yourself again. install the PSU into the case and secure with the 4 mounting screws.
plug in the power cord and ground yourself again from now on after grounding, unplug the power supply cord from the wall.
if you move your feet, or shuffle in your chair, plug in the cord, reground yourself and unplug again.
connect the power supply to the motherboard by the 24 pin and the AUX CPU power connector, install the GPU if one is selected, and install the drives with the supplied mounts in the case. connect the front panel connections to the case according to the manuals.
if you move your feet, or shuffle in your chair, plug in the cord, reground yourself and unplug again.
if there are any other peripherals, like wifi cards or sound card install and secure now. verify all power cables are connected to the motherboard and the GPU if needed.
the system can now be booted and the BIOS adjusted if needed (refer to motherboard manual) then an OS installed. when you are sure the system will need no more working/tinkering you can install the side panel and close the case. you have now assembled a PC.
end canned rant
this was written earlier but with the videos you watched the grounding tips will work well.