I’d put ATC, Low-Ki and Barracuda 4, all in a similar category as the wing is connected to your ankles as compared to a beginner suit like the Swift or Piranha where the wing terminates just below the hip. Being connected to the ankle vs hip puts more fabric behind you at pull time as well as restricts arm movement after deployment. Small suits also let you make bigger mistakes when flying with the wings as big inputs mean less drastic movements. Being connected at the ankle means leg movements and lower body position is more critical.
I wouldn’t say the B4 is any more or less beginner friendly than the ATC or Low-Ki. However, if you’re picking from those three, you probably won’t notice much difference unless you put some serious time in the tunnel with each one. If you’re just flying around the sky with friends and learning, you can’t go wrong with the B4. However, I’ll restate that you might want to also consider what your friends are flying for compatibility.
Adjustable internal wing pressure is just a zipper in the arm wing that you can open or close to make the suit more or less pressurized. More pressurized is slightly faster. Most people just keep them zipped up. I don’t know anyone who uses them to adjust for anything specific. I once flew a Havoc in the Stockholm tunnel and didn’t notice one of the wing zippers was zipped and the other wasn’t. I felt something was slightly off, but it wasn’t a huge problem to correct with minor body position change. After that session, I got out and checked the suit and zipped it back up. I probably wouldn’t have noticed if I weren’t in the tunnel.