[3.P] The Summoner's Handbook: A Guide to the Pathfinder Summoner

[Andvare]

You will need arms in any case, as you can't cast somatic component spells without 'em.

Be very careful with dumping con. When your eidolon goes, so does that extra hp from the eidolon's con, and that could kill you instantly at higher levels.

The only way you can heal a synthesist's eidolon is via the rejuvenate eidolon spell chain, so this is a necessary spell.

Beware of dismissal and other spells that can remove your eidolon instantly. Though they do require a will save, they can gimp you quite thoroughly (you still have summon monster to fall back on though).

You are an excellent front line fighter. You should have more hp than anyone else (effectively getting almost double con bonus on each level, plus the extra, if only d8, hit die). Your AC can also hit a very high number, though this is mostly natural armour and spell buff armour, and you will probably have an appallingly low touch AC (like a regular full-plate fighter often has).
Your damage potential is also quite high, but can be hampered by damage reduction.
The highest damage potential is clearly the Kali multi weapon double slice type (be sure your GM accepts that you can take double slice with multi weapon fighting), as the only limit to how many attacks you can have in one round with a weapon, is your evolution points. However, this build is severely challenged by DR.
A more typical build is the centaur build. Pounce, one huge weapon and as many natural attacks as your level allows. Extra evolutions points used to buff str, con, dex and armour and other goodies.
But the possibilities for a build are rather large. You can easily do a trip build, or a battlefield control fighter (with grease and a high cha for intimidation so antagonize and dazzling display both are very viable) and so on and so forth.
Your role is somewhat locked in as a fighter, and probably a melee fighter. But other than that, go nuts.

Edit: Just realized you actually didn't ask for advice, ah well, it's there now.