No equipment, no levels, and no experience dealing with the significantly higher powered mp enemies will make you feel sort of outclassed. I recommend leveling up a heavier power using class like sentinel or engineer, something not so weapon dependant. Get a few levels, and you should have no problens dropping bronze mobs with ease. Once you upgrade a few weapons, you can play with different classes where your lack of skill can be compensated with a good weapon. Great guns to play with are the carnifex (arguably the best gun for power heavy classes), the widow and black widow, the geth shotgun, and if you ever obtain it the saber. When it comes to multiplayer, powers become very mandatory, so try to always keep your weight low for the recharge boost.
Alot of people argue what is a better way to spend credits. I personally say avoid veteran packs, spectre packs are far more efficient ways to burn credits, especially since you will generally get at least one uncommon (silver) item and a guaranteed rare (gold) item as well, not to mention 5 of a random consumable item like rockets or medi gels, and generally one level three bonus mission item like ammo or rail amps. If you feel like you're missing out on items, I'd tell you to burn out some credits on recruit packs. You'd be surprised how effective a max level predator or mantis can be at times.
Also, tomorrow you get a victory pack for our success over the weekend promotional event, so you may score something nice there.