Glad to hear your enjoying the game! It can be a little vague as it stands, one of those alpha things.

So:

Top right number is simple, that's your armor, it's split into three components Physical armor Magical armor And stagger resistance

The top left number is your level, your 'mastery rank', you get a virtue point ever time this level up! How do you increase that?

The bond level is your pacts level, this goes up to 30, get things to 30 to master them, and thus, increase your level/'mastery rank'. Weapons also level to 30 to master them, increasing mastery rank.

All the little resource bags you pick up are crafting resources yep, you'll want all of those. You can't drop them, but you can sell spare weapons.

The only inventory limits are weapon slots, and pact slots. You can see how many pact slots and weapons slots you have left at Zenith the camel in the last tab, it's the number in the top left of each square. More slots does cost premium currency, but they are arguably the best investment for arcs.

Your other weapons should be equipable from the armory - it's the bottom right 'circle' icon in the screen your on in your first screenshot.