The first thing you should do is check your jointer fence to make sure it's dead on perpendicular to the bed. If not 90degrees, then you're already starting in a deep hole.
I don't use biscuits and rarely use cauls. I use quick grip clamps to align the boards at the panel ends. I alternate clamps top and bottom and avoid over tightening. I've never worried about alternating the grain (not convinced it helps, and it would often interfere with the desired face grain pattern).
On extra wide panels I do the glue up in sections, e.g. if it's 6 boards I'll glue up 3 pairs of 2 boards, joint and plane each before doing a final glue up of the 3 sub-assemblies. I've found that doing this improves my chance of flatness.
Even with the best practices, it's darn near impossible to get all panels dead flat. I don't worry about minor deviations; most of my panel work gets attached to an apron which makes it easy to pull flat.
Hang in there and keep tweaking your process...you'll get it figured out.
Scott Vroom
I started with absolutely nothing. Now, thanks to years of hard work, careful planning, and perseverance, I find I still have most of it left.