As you've seen, GUE Fundies is the oft recommended answer when people have little else to contribute. GUE is a miniscule community, especially outside the USA. I will agree the GUE divers that I have dived with are impeccable in the water, but their dive planning and decompression theory wasn't inspiring. GUE divers go to trimix quite early, but they also buy Helium at USA prices or they spend a fortune. A mate of mine spent AU$1400 on gas for a weekend of GUE diving. He left Sydney a few years back and lost his cert for not doing his (?25 per year?) dives with GUE groups using GUE standard mixes, even though there was no GUE presence. In regional areas its just not viable, but it is certainly held in high regard by those inside the community.
As an AN/DP diver you've got a ways to go before you can add Helium, unless you do Helitrox, which is within your scope if your Instructor will run it for you to breather hyperoxic mixes. Trimix breathes lighter, much easier at depth and you'll shed CO2 better. Its a good call to use it if you're qualified, but, its expensive. If you go somewhere like Bikini Atoll, only CCR gets Trimix as they cannot carry enough gas. All the OC divers are on air at 52m depth and they're fine. Just cruise, don't work yourself hard and stay on top of your breathing rate. If Trimix 75 is your goal, get the elearning and start the process. Trimix is an awesome course, just watch out for the gas bill at the end.
Holding depth on deco has a lot of feel to it. A lot of tech divers dive regularly, many of us dive when we can. The first few dives take a bit to get the feel back, always do a shakeout dive first and go easy on yourself. Put up a DSMB and hold it out at arms' length so you get a feel for the changes, then close your eyes and try to feel it with your ear pressure, your arm angle, etc. Its 1000% easier to maintain depth in horizontal trim so work on that. Give yourself time, patience, and hours in the water. Guys that do 400 dives are year are superb. Guys that do 25 tend to look amateurish.
As to some of the other advice here, you have to work within your cert level what gases you can get locally. Deco on EAN 50 works fine for 40m dives. EAN 80 is better, 100% O2 is really only practical when you level up to carrying two deco tanks. Check your dive plans with a few mixes. For all the waffle about 80% being a stroke mix, the difference is minutes. In some locations the absolute best mix you'll get is 92% and again, the difference is a minute or two.