Building a scorpion eidolon

[xDemoquinx]

What else would you add to this base for a scorpion model?
Assuming Wild Caller Summoner with favored into evo points

Quadruped Base
Bite
Legs x2

Str 14 (22)
DEX 14 (17
CON 13 (18)

22 points total at lvl 12 (not using feats yet)
4 Large
2 Arms
1 Pincers
2 Grab (Pincers)
4 Poison (CON) 1d4 Con/
2 Tremorsense
1 Tail
1 Sting
1 Climb
1 Pounce
2 Rake

Since i am taking the arms evo, can i add a slam with the pincers? Or would i need to add another set of arms for the slam. Same thing for the tail slap. Separate tail?

What feats would you suggest for Mr. Pinchy? I am thinking of the grapple feats to start off with but there could be better. How else can i get that poison dmg/ DC more effective?

If i wanted to full attack, could i use my pincers first? Hoping to succeed the free grapple check. If not how would the sequence work out?
Could i full attack with just my secondaries and not take the -5 for it?

[lemeres]

I am pretty sure it is one or the other on the arms thing. You only get one attack per appendage.

I think the slam evo is meant to take up both arms...but it doesn't exclude using other evos. So do a crab on this and give it a big bashing claw and a tiny pinching claw.