YES and NO ;)

I like the idea to require some kind of rope or holster to attach weapons but I totally dislike the idea that I am only able to carry one main gun on my back.

I have a couple of old and new-ish rifles and I can carry them ALL at the same time with ease.

Years ago I crafted some fancy 'improvised' leather sling holsters which allowed me to carry 5 rifles on my back, all fully protected against unintentional movement and even to damage (to some degree) - Was pretty neat because it also allowed me fast access without having to fiddle around while drawing or putting them back. It felt like being some kind of Mad-Max-style outlaw survivor :D

The number of weapons (or any equipment) should be determined by weight and not by "slots".

More stuff means faster exhaustion and less agility

(edit)
come to think of it, a weight-based system would even add a whole new level of character customization:

• A sick/injured player should be weaker than a healthy player.
• A notorious camper should suffer from muscle degradation and therfor end up with less stamina and agility if heavy loaded.
• A notorious road-runner should build up stamina over time, being able to quickly move heavy loads for a longer dinstance.

...this could go on and on but I guess you get my point