Good that you can wavedash. That's essential for his wave magnet stuff and movement in neutral. Without Lcancels, Lucas is very hard to play at top levels given that he has poor auto cancel windows (see Marth's Fair, Fox's Bair, etc).
As for DACUS, I set my R trigger to Attack. This give a slightly easier time on your finger (trying to hit a button is already hard enough on your fingers, and the Z button will begin to hurt even more over time). Also, if you whiff a DACUS attempt and dash attack rather than grab, there's way less punishable frames and dash attack sometimes has the potential to hit your opponent by mistake.
If you're accidentally doing dash grabs as you say, try to make sure you hit the dash attack (Cstick input) then up. Slow down the grab input. I used debug mode at the beginning of 3.5 after DACUS windows were changed for Lucas. It helps you break down frame data and understand DACUS better.
In Project M, his side special is called "PK Freeze," PKF for short. DJC PKF simply requires a slight tap of the 2nd jump input, rather than holding the jump button while using a side special. I can't say too much more than that as I don't know what your inputs look like in-game. If you provide video, I might be of more assistance.