A few points, Jack. First, you don’t want to pick up just everything you find. Some items are worth more than others, and some items aren’t really worth bothering to pick up. As a general rule, body amor is worth a good bit, scepters, wands, and staves are worth a lot if they have plusses to skills on them, but not otherwise, colored items (magic, rare, unique, or set; blue, yellow, gold, or green respectively) are worth more than normal items (white or gray), and items with weird names are often exceptional and thus worth more (but you won’t be seeing any of those for a while yet, at least not until Act IV). Cracked, damaged, etc. items usually aren’t worth the bother, unless they fall into one of the above categories. But your general strategy is sound: Gather loot out in the wilderness until your inventory is full, then portal back, sell or stash the loot, stash the gold, and re-supply.
You can buy a Tome of Identify, which holds up to 20 identify scrolls and only takes 2 spaces in your inventory, and a Tome of Town Portal, which likewise holds up to 20 Town Portal scrolls. If you don’t mind buying a new Town Portal scroll every trip to town, you can save a little space by not having a tome, but that’s a hassle. If you keep two or more of either scroll type in your inventory, then buy tomes and save some space.
Don’t bother stockpiling keys. You can carry twelve in a stack, which’ll last you for a few trips out into the wilderness, you’ll find more all over the place, and they’re cheap to buy if you start running low.
High damage on a weapon is nice, but attack speed is nice, too. You might be able to find a weapon that’s better, even if it has lower damage, if it swings faster than a polearm. Of course, later on, you’ll find weapons that both do more damage and swing faster than your current one. Also, the polearm is two-handed: With a one-handed weapon, you could add a shield or (since you’re a barbarian) another weapon. On the other hand, polearms have longer reach than most melee weapons (this will be very useful if you decide to go with Whirlwind), so it’s a tradeoff.