does it matter if i have a Patriot Viper Elite 8GB (2 x 4GB) DDR4 2400MHz already installed?Will it work, yes.
Note: Due to limitations imposed by the B250 chipset, ram speed will be limited to 2400mhz.
Because of this, buying a 3000mhz kit is a waste unless you are planning to upgrade to a board with support for 3000mhz ram.
cus i like to wast money am i okay to buy https://www.amazon.ca/gp/product/B079NQHWMG/ref=ox_sc_act_title_1?smid=A26PVB3960EU85&psc=1 if i have the (red version) thats 2400hz compared to 2666 https://www.newegg.ca/patriot-8gb-288-pin-ddr4-sdram/p/N82E16820220996?Item=N82E16820220996Yes, it does. Mixing different kits of ram can cause problems including no boot.
I would suggest buying another identical kit as what you have.
What did you want 24gb ram for anyhow?