is it possible for a newb to be really good at umvc3?

you can become really good at Umvc3 but it will take a while depending on the characters.

everyone started out as a newb so i assume so.

It depends on the characters you pick. Straight from the start, Hulk and Sentinel will be your beat buds since they can do loads of damage from the simplest of combos; they also have great normals which are great for starting combos. When you get to a certain ability level, you can just scrub out and pick top tier characters with practical and damaging combos like Vergil and Dr. Doom. Being successful in umvc3 is based more off on how your 3 characters work together. Dr. Doom can basically fit onto any team since he has 3 great assists which every character cam benefit from; and he also has a TAC infinite (quite advanced) which is basically when your point character does a combo and then (in simple terms) switches into the next character in the air to continue the combo. Then, the character can do an infinite! Another way for an intermediate player to be good is to use Morrigan and spam projectiles (but be warned, her combos aren't that easy). See what works for you and good luck! :3