I had my very first MP match earlier this morning, and I can see it being challenging, but it wasn't too punishing for me, honestly. It probably helps that I was using the Angara Insurgent, who I think is a good "beginner" class: his shield boost can save your ass, his trip mines downright one shot minor enemies(on Bronze, anyway), and his turret is a good way to distract enemies. I only had to use a health pack once, and I didn't end up dead and needing to be revived.
I'm sure Silver and Gold will kick my ass, but I plan on leveling my classes in Bronze until they're a solid level.
My current weapons for each class I play are the Falcon assault rifle(which is a grenade launcher, I think) and the Equalizer pistol(Remnant machine pistol). I do have the Pirahna shotgun, which I might use on a Krogan Vanguard whenever I unlock one.