Confused about Eidolon's number of attacks, penalties, etc.

[O1av]

Hey there, I'm new to PF and DnD in general, and I have some questions about how many attacks an Eidolon can actually have and what penalties apply.

The Eidolon will be starting at level 4 (7 evolution points and 2 feats).
Take for example a biped Eidolon which gets free claws, arms and legs.
-If I add another pair of limbs (2p) and another set of claws (1p), are all 4 of my claws still considered primary attacks, and can I use all of them with a full attack action without any penalties?

And what if I add another set of arms (2p), get Martial weapon proficiency (Greatsword) and use a greatsword, will I be able to attack with all 4 claws (with normal attack bonus) and my greatsword without penalty, or did I overlook something?

I had assumed that if I added yet another pair of arms (2p, now at 7p) and bought a second greatsword, I would need Two Weapon Fighting and the penalties that follow from using two weapons, is this correct?

(And just for laughs, if I have 8 arms and 8 bastard swords (with prof.) and Two Weapon Fighting, do I suffer -6 on half and -10 on the other half or more?)

I'm not sure what the Multiattack (monster feat) does either...
I would really appreciate if someone could clarify it for me, and I apologize if my questions are stupid or get asked often (if so, could you point me to a thread?).

[Mojorat]

you pretty much have it right on the weapon parts. the claw attacks are all primary attacks so it would have 4 attacks. however natural attacks used with weapons makes them secondary weapons -5 tot hit and half strength to damage. several of the eidolons natural attacks are by default secondary. multi attack reduces the penalty to make secondary attacks to -2.

[Rellen]

First off a 4th level eidolon is limited to a maximum of 4 natural attacks, which does not include attacks made with weapons. So in theory you could spend 4 points to get two additional sets of arms, 1 point on claws, and two points on simple weapon proficiency.

Wielding a melee weapon would make all four of your claw attacks secondary, meaning they are at -5 to hit. Multiattack would reduce this penalty to -2, but taking it as a feat is probably unwise since you get it for free at 9th level and get nothing to compensate if you already have the feat - a kind DM might house rule this, but it would be a houserule.

You could take 2 weapon fighting - you don't technically need it, but you do if you want them to be worthwhile - to give your eidolon a formidable 6 attacks, but you would somehow need to get a 15 Dex which will be tough with the biped form. You might actually be better of getting as many weapons in hand as possible and taking Multiweapon Fighting, which requires a dex of only 13 and 3 or more arms.

With multiweapon fighting the penalties are reduced by 2 with the with the primary hand and by 6 with all of the offhands. Note that you can only ever have one primary hand, its not one from each pair.

So for a 4th level eidolon you could spend 6 points on limbs arms, one point on bite, and use your feats for exotic weapon proficiency say Sawtooth Sabre (good because its essentially a longsword you can treat as a light weapon for lower penalties) and Multiweapon Fighting. This would give you 8 attacks at -2 your regular attack total with the Sawtooth Sabres 1d8 19-20/x2 and one bite attack at -5. Not too shabby, but very expensive when you start needing to enchant all those blades. That's assuming that you can use weapons in the hands with claws, but I think that's fairly reasonable I'm sure there is precedent in the Bestiary somewhere.