I've spent some time on this game so I feel I can give some hints. It's been some time but I recall most of it from the time I've been able to 1cc (and score too but I'm top of the 3 people who tried seriously outside of Japan).
First of all the game looks unfair by pouring tons of messy patterns, but keep in mind there is no rank or random shit to master the hard way. It's very deterministic in a lot of ways. Saying that, I can tell that even if (like many) I don't fully understand all the clockwork inside, I ended up building solid strategies and scoring routes in time by just... playing.
Second of all the game looks unfair by not giving any extend (I just hate that). So treasure your life and focus on dodging (ie: don't play a Yagawa game casually in your freetime while trying hard Night Raid).
Stage 4 boss is a huge difficulty wall. Bullets are super fast here, but as it's always the same pattern you can find a safe-ish strategy pretty quickly. This is THE moment in the game why I used save states to experiment the most, and where I use my first strategic bomb (because I honestly could not find a safer strat).
This and last boss are the two moments I consider spending lives and bombs. I remember allowing to lose 1 life anywhere else (costing a big stress during final boss), and consider the run gone forever if I lost 2.
About the hug launcher and the "keep pressing C" thing I use it (on stage 4 boss and in another place iIrc) to move the destination point after the bounces. For stage 4 boss it's to land in a "safer" spot during a vomit-style pattern, and in a stage (probably 2?), to be at items falling point and optimize the pickups route. But you can easily forget about it, I do it mostly for style. But the main usage is to milk enemies as they release items when they are hooked until you reach them. You can see it in action here
https://www.nicovideo.jp/watch/sm16561255 on the stage 1 boss. Timing the duration to milk and bounce just what it takes to land the last hit on the core and kill it is very tight, but proof that this game is definitely waaaaay more subtle than it looks.
As for the combo you can make, I also guess the gauge depletes slower if you move a lot. The replay you can find on NicoNico has 30+ combos all the way, and knowing the love of Japanese players for autofires, I'm pretty sure there he's using a button to move in circles at max speed (like the "autoroll" hacks on Psyvariar cabs I've seen).