There's a lot of classes which can gain access to shadow spells one way or another. The better shadow spells are higher level (to an even stronger degree than normal spells) so you're looking at a full spellcaster, not a 6-level one. Sorc/wiz/arcanist is obvious but cleric, oracle, shaman and witch work too. Also - starting at 1st level you're not going to do a lot with shadow for a long time, just so you know. 4th level spells (character level 7-8) are where it gets interesting.
A fetchling arcanist has a useful alternate favored class bonus for shadow spells. On the other hand fetchlings don't get an Int bonus which is annoying for the purpose. A wayang wizard or witch could be very good at this. At the other extreme while they don't cast a lot of shadow spells a shadow bloodline bloodrager uses shadow a lot.
Be careful with the use of metamagics in general - since these spells are heavily level-dependent and high level anyway you may be better just to cast the highest level spell you can without any use of metamagic. Except for metamagic rods (of persistent spell?) anyway.