| Jofarin |
The Summoner's two arms don't count.
Why?
Multiweapon Fighting gives one attack per arm after the first; only the primary hand increases with BAB.
Yes. On lvl 10 you get 14 evolution points resulting in 14 arms resulting in 2 main hand and 13 off hand attacks (+2 summoners hands gets to the 17 I mentioned).
At lvl 1 a dwarven biped eidolon synth can spend his evo in 2 extra arms and a nat AC raise (and multi weapon attack) for at least 4 attacks with +2 atk and 1d10+3dmg (1d8+3 if you can't afford enough dwarven waraxes and can't combine them with your claws) at +9 AC (if you cast mage armor) and ~11HP.
...while having stellar WIS, INT and CHA and being able to cast like a normal summoner (or maybe better, because you can spend EVERYTHING to push charisma).
At 2nd lvl you can either get 2 additional attacks or +4 AC.
If you don't take the biped, you can even push in pounce and will only have 2 attacks, but even at a charge with 40ft speed. But you'll lose 1AC, 1atk and 1dmg, so I'll suggest going biped.
I excluded the possible bite attack, because I don't know if you can bite and strike with weapons on a full attack.
IF you can use the summoners arms and the natural attacks combined with the weapons, you get 6 attacks on biped and 5 on quadruped.