kinevon
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Since it is a first level spell, essentially, yes. You can even purchase one for 2 PP.
No, you don't combine the HP, the Eidolon's HP are considered Temporary HP, so have to be healed in a a different fashion than you PC's regular HP.
Also remember that, if your Eidolon'a HP, as your Synthesist Summoner's temporary HP, goes to zero, your Eidolon/Synth Suit, goes away. Which is yet another reason why the HP are handled separately.