Hello, I'm about to buy 1x8 GB of RAM DDR4 hyperx fury 2400mhz, for now I have installed 2x8 GB of RAM DDR4 hyperx fury 2400 mhz. My question is... It will be a problem if im using 3x8 GB of RAM? Every kit is bought separately but the same model.
It will likely be OK, but it's for that reason that most people recommend buying the RAM in sets instead of one at a time for the chance that the chips could be different (despite being the same model). I would still recommend getting a 2x8 so that everything is equal across the board. I'm unsure if your machine will handle having an odd number of chips to work in dual channel memory, someone else may be able to comment on that.
After you get it I would recommend running memtest86 and Prime95 Blend or similar that will stress the CPU and memory to make sure that everything works well together.
If you buy 3 sticks, you will run in what is called 'mixed memory mode' I believe. Basically, you will have dual channel for two sticks on the same channel and single on the one left alone. This can cause instability. You always want to buy in pairs.
I also question why you need more ram... are you going over 16GB? If not, adding more will not help a thing. Now, if you are very close or going over, it would help.