I'm with Kayelle. I've been cooking for two for nearly 25 years and have never had an issue with too much in the crock-pot, especially this time of the year when everyone is so busy with holiday activities and preparations.
I don't think there's too much to consider with the cooking time when you prepare small portions in your slow cooker. You want to be certain the proteins (meat/poultry) are thoroughly cooked. However, with reduced quantities, you could encounter either overcooking or dryness, in spite of being in the cooker.
If you are new to cooking or, as you say, using a slow cooker, give yourself some time. If you are like the rest of us, you'll have more than one in no time. I do. Several different sizes, which might be a good initial solution for you.
These appliances aren't too costly any more and, often, can be had for even a few dollars at thrift stores. I purchased my favorite 5-quart one at a senior citizens yard sale about 15 years ago...for $2.