"is it worth it" questions are really tough to answer. For everyone, the internal calculus that makes it worth it is going to be different- and pretty arcane at that.

I honestly suspect that, if there's only one project (the engine), that you're going to finish- or not even start, after having learned the basic lessons (and there's a lot of lessons to learn. And keep learning... new materials all the time, with new properties new gadgets.)

If the motivation is to 'learn 3d printing' ... it's probably going to be something that stalls out. Which, if it's something you keep coming a back to.. that's okay. I would HIGHLY recommend looking into your local libraries, or for a local hackspace. many- probably most- public library networks will have at least one available for use. They may even offer classes.

just be sure to learn the limits of what can be printed... and what can't... feel free to ask.

I second comment from overzeetop's comment about prusa being entry level. you can make a creality machine print as good... but then it's no longer a creality machine. The prebuilt prusas from their shop is an amazing starter printer. and with some work and a lot of practice... will likely be capable of meeting demands in PLA, PETG, ASA, TPU, and with modifications all but the most troublesome of specialty filaments. (also the prusa community is wonderful. just saying.)