How much RAM you need depends on what you want to do, some reading here:
If you want to cobble mobile games together, you may get away with 16GB. If you’re solo making an MMO, you’ll need more. If you want to take advantage of the UE5’s advanced features - well, check the link. 48GB may not be enough… But it’s Early Access, things may change.
48GB > 32GB obviously.
With a single stick, you’re running single channel. Lowkey irrelevant in certain scenarios, quite noticeable in others.
Intel platforms have Flex Memory Mode so running 1x16GB + 1x32GB should still give you some benefits of the dual channel (conditions surely apply here, though). Is that important to you?