NO COMPOST ANYTHING! Sphagnum peat and silica sand/perlite or a combo of all 3. Mostly peat. Fertilizer is usually one of the first mistakes, tap water is another. I start seedlings in a 2"wide X 3" deep pot. Not sure what plugs are but if the rhizomes are bigger than 3/4" I would give them about 4-6" for each and maybe more.

If you want to kill your plants, using manure and compost peat is the way to go. Usually compost peat is processed humus. Carnivorous plants are not garden plants!

It has to say sphagnum peat moss and avoid sphagnum peat moss that have additives added to it like humidifing agent (a chemical that allows peat to become wet quickly) or fertilizer.

Same with perlite or sand.

I advice you read Peter D'Amato's book: Savage Garden. It's a popular book that explains how to grow carnivorous plants.