Are you wanting to build a flying model or a static model.?

1/48 is a bit small for a flying model I think, because the weight of constructing it with a power source would mean a high wing loading which would necessitate a high flying speed to work at all.

That drawing is of a rubber powered free flight model designed for traditional balsa and tissue construction.

To go down the road of making a plug, then a mould, and then actually moulding something is a lot of time consuming work if you are only going to make one model.
Getting all the stuff together can also get expensive.

I'm not trying to put you off because whatever happens you will learn something and I wish you luck with your endevours.

Been there and done that a few times.