I can comment on the capricorn tube. It may have “technical” advantages, but honestly most ptfe tubing will work just as well. Though capricorn does seem “more preemo”. In the end i wouldnt expect a performance change useing capricorn or shelf brand ptfe, so long as its inside diameter fits your filament.
As for the beat paste @LEGOManiac has a good point. Its not “nessisary” but it wouldnt hurt and can help if your heater is smaller than the microswiss block. Im going to guess though it should fit fine, unless your current hotend is covered in burnt filament, therefore making your heater cartridge and thermister slightly bigger.
One advantage i could see to useing thermal paste would be to more easily do hotend quick changes. I read somewhere that having a few microswiss heater blocks set up with different nozzles pre-done would be faster/better by just swapping the thermister and heater cartridge. This would be beacuse its just a grub screw holding it in iirc. So the thermal paste could make swapping the heater cartridges easier.
The downside to the thermal paste is itll be messy.
I got a used microswiss and couldnt get the heater block to seat correctly, so regardless of our advice. I do strongly suggest to pay particular attention to how you assemble it. Once its all good and printing, id keep an eye on the top of the heater block for filament to seep out.
Good luck and hope this helps.