How does weapon and character levelling work?

Good question. Would like to know more about this too. My 10 hours went by sooo fast. From what I recall, you receive weapons and character XP while playing, but can also receive level ups for weps and characters in crates too (in addition to your earned XP). Anyhow, sure someone who has more information will share.

I will ask though, is it best to focus on buying basic crates for now? Seems like the right thing to do, similar to ME3MP. Buy entry level crates for a while to get the common weps unlocked and leveled up fairly quickly (as well as character level ups and unlocks). I was watching some MEAMP on Twitch yesterday, and saw a player who had saved 100K creds and bought a premium pack. They got the Falcon II which is a decent weapon, but the rest of the pack was basic crate items.

It's not complicated. Basically getting your weapon and character from levels I-X give them slightly improved stats overall. Characters also get extra skill points and visual options. And yes, you can only get them through crates. The rarity goes: common, uncommon, rare, ultra rare, with them being harder to get the more rare they are.

Once you reach Rank X of a given Card, that Card will no longer drop yes.

You'll still see boosters though.

stats/stats/skillpoints

each rank is more better than the previous rank

Weapon mods go up to X now.

Can't wait to get a Smart Choke X so I can turn my shotguns into snipers.

That depends on each gun. That's the beaty of it.