[koz]

My suggestion - get a standard Large Alice pack with standard straps, frame, waist pad. It's a good ruck and will serve you well. There are some riggers (there was a good guy at Gen Jackson's @ Ft. Bragg) that do mods on rucks if you want to add extra pockets.

If you show up at a new unit/job with a completely modified ruck, "your soldiers" will notice.

Like Blitzz said, get used to carry heavy loads or medium loads to get your shoulders, and back in shape. I'd avoid jumping right into the heavy loads and trying to run with a ruck on.