Degraded quality is down to the choice of codec and settings you use to export your edited video, rather than the software specifically.
I can use top end software like Adobe Premiere Pro, and still end up with degraded video quality if I choose the wrong codec to save as!
I've no idea how good WMM is these days. Have you had a google around for free VE alternatives? Something like https://www.lwks.com/ may do?
This is one of the best first coasters I've ever seen, aside from the wonky supports (which have already been pointed out) and the strange colour scheme - normally I prefer the ties and the rails to be the same colour.
Trackwork is pretty good, a fun and unique layout with some thrilling moments. Some airtime moments wouldn't hurt.
Catwalks are needed on the lift and brakes for sure, I'm not a huge fan of jumping from a few stories in the air during my evacuations.
Bonus points for heartlining, which is overlooked far too often by newcomers to the software.
In terms of the video, I'd disable the "look-ahead" effect while recording for a cleaner/more professional presentation. Also, I recommend Handbrake for all your video conversion needs in the future, never had any issues with it and it shrinks file size like a dream (no, I'm not being paid to advertise).