Hello
I'm a new player as well, and I've decided I would like to jump into Malifaux by joining Team Marcus.
I personally prefer to buy my stuff in a bundle, to keep down shipping costs, and I'm going with the new plastic stuff by Wyrd, can't deal with metal. Wyrd just sent out a newsletter that they'll be releasing new stuff soon, including stuff that can be used with Marcus, so I'm delaying my purchases until then.
My current purchase plan is:
Marcus box set
Dawn Serpent
December Acolytes
New Canine Remains (plastic)
New Molemen (plastic)
And I might double up on the Rattler and Cerberus so that Myranda can shape change while the other one is still on the table.
Molemen, for the reasons already outlined above.
Canines, although not Arcanists, and ignoring the fact that they're zombie dogs, will be a good fit for Marcus. Cheap, fast, can take a hit or two, can run schemes. Although they seem to not be good at fighting, they can debuff defense by standing within 1" of an enemy model. And if you get lucky, you can infect enemies with Rabid (Beast + -1 WP) which Marcus can take advantage of.
Acolytes, although not Beasts, I will paint them in woodland colors so that they can be woodsmen or hunter types. I'm bringing them because they have a gun, which most Beasts of course do not have. They're not so bad in melee either. They can deploy anywhere on the field that's not within 6" of the enemy deployment zone. And they have a tactical action, Smell Weakness, that can strip away an enemy's armor and hard to wound. It's not a Ca action, it just happens, which is awesome. Suddenly that Peacekeeper doesn't look so tough with his defensive traits stripped away.
Dawn Serpent, one of the few Beasts with a gun and can hit hard in melee too. His Counterspell ability will make him a huge pain in the ass for Ca heavy crews, since he can strip away triggers and outright stop some spells from working on him. And he can heal himself with his (0) action.