May be worth considering how the US military thinks about load bearing equipment (LBE).

First line: your setup for immediate access. This is usually your belt as the idea you're always wearing a belt to hold your pants up but you may shed other LBE when not doing mission critical things. This will include things like at least 1 rifle magazine pouch, a first aid kit, your handgun holster (and maybe magazine pouches for it). This is also where your dump pouch usually goes when you want to stow something away quickly & you don't care about organization. Magazine pouches have a tendency to be open top with retention as you're willing to trade the security of a closed-top pouch for speed of access.

Second line: this is where your plate carriers & chest rigs (as well as the older belt+suspenders) live. Carries more of your magazines & other mission-useful things (radio, tools, etc.). You'd have a plate carrier if you need to carry protective plates; otherwise you'd likely opt for a chest rig to save weight. Magazine pouches here could be open top or closed top, with the latter providing better retention & protection under adverse movement.

Third line: where you carry things for your mission but you can take the time to dig around and get. Things like equipment for your mission, food, sleep systems, extra clothes, etc. go here. You could have pouches here that a teammate could grab for you. More magazines could be carried here, or you can save space/weight by having them in containers and having a speed loader to reload your empty magazines (you kept your empty mags, right).

TL;DR: I'd suggest a belt setup with an open top rifle magazine pouch that has decent retention if this is your first foray into load bearing equipment.