And NO ONE should tell you it's OK as this is exactly how the issues happen. "It should be fine" is not good enough. But in a lot of cases it works out but pity the people that write it will be fine and it is not.
In short, your choice.
Back when I built the PC that I have, I included modest parts with the idea of upgrading it down the line. I currently have a 4GB stick of RAM from the Crucial brand running at 2400mhz. I want to upgrade to 8GB of RAM, but I have a couple of questions that I haven't been able to answer yet. I'd like to add 4GB in order to take advantage of dual channel and I found RAM from the same manufacturer, running at the same frequency, with the same voltage and also 4GB at a pretty cheap price. Should that be a problem if I get them separate? Because I've heard that you should always get RAM in pairs to make sure they are the exact same model in order to avoid compatibility issues down the line. I could get an 8GB stick, but that would mean getting rid of the stick I have (so losing some money) and not taking advantage of dual channel. I'd more than appreciate someone else's expertise on this since this is the first time I've added RAM to a computer. Thanks in advance!