What's the max amount of guns a character can carry without making it look too unrealistic?

2 longarms and 2 sidearms.

After this point it becomes almost clownlike.

2 handguns a rifle a knife and ammo is probably all you could carry without being to weighed down.
A loaded 1911 weighs about 3 pounds, an AK47 is about 10 1/2 pounds, and a KA-BAR combat knife is about a pound. A 30 round clip for the AK is about a pound, and a full clip for a 1911 is about a 1/2 pound

As long as it's not magically glued to back or legs (like 99% of games where they show guns on character).

Also if you plan to make your character wear loads of weapons, you might want to use polymer stuff instead of iron, and caseless ammo, if you don't care about their drawbacks.