I have not used those packs but I think you are on the right track. The belt only style packs just can't carry much. I had a believe a Jan Sport convertible pack that would expand from a lumbar pack to a conventional pack and it was a good option if bulky extra clothes were needed.

Here is an inexpensive option that looks like it would cover most of your needs. https://hornhunterpacks.com/product/typical-7-pocket-fanny-pack/ I like these more minimal fanny packs that don't have bulky side pockets that get in the way of a rifle or pistol. I don't see an option for adding pockets but bulky jackets and things could go above the pack. I like the simpler packs as too many pockets can make it harder to find stuff and then I never empty them and keep adding things until full. At the end of the season I find all sorts of things like really dry sausage, year old granola bars a stash, of dead batteries and cartridges. The Horn Hunter is inexpensive enough you could get a second larger one for winter time hunts.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli