What exactly do you mean by necromancer that is a summoner? A summoner class character that has necromancy, a necromancy school wizard that can also cast summoning spells well, or just a character that can both do summoning and necromancy?
As for necromancy clerics, you already chose the core class that most lends itself to having an army of undead minions, so that's good. There is an archetype that lets you have an undead companion too, should you fancy that.
But let me give you this advice: A character lugging around a lot of minions and companions tends to be time consuming in combat and quickly falls into disfavor with the rest of the players.
Clerics who worship Pharasma, or other death-minded anti-undeath powers, get a modified Death domain as one of the ones to choose from.
Otherwise, are you using necromancy in the 'I know how they work' sense? Or in the 'fight fire with fire, and fight fire skeletons with blood skeletons' sense? For the latter, there's a guide to undeath in general ... but mind the advice above. Don't make your GM worry about fifty crappy skeletons. It's not worth your time either.
Oh, and the guides I've seen generally note that along with Knowledge (Religion) for knowing about undeath, you'll likely want to invest in Diplomacy. 'Oh, that skeleton army? It's for the cause of good! Really! Smile, guys!'
Bones Oracles make awesome necromancers. Undead servitude makes you really good at capturing undead and repurposing them. I recommend taking improved channeling and the sacred conduit trait to boost the save DC by 3.
Then take Raise the Dead and Abundant Revelations (Raise the Dead). Now you can summon a few skeletons or zombies a day or capture a bunch of undead and send them to do battle against other undead without ever casting animate dead yourself. It's a win-win-win scenario, and if youre a gnome you can take the alternate race trait that boosts your necromancy spells' DCs (almost all the bones mystery spells are necromancy). My favorite thing about the build is that Oracles can be good aligned and still channel negative energy and cast evil necromancy spells.
