@Cript: CHASSIS is actually your armor, since you can't equip a normal vest like a humoid could.
Lv. 1 Ceramic Striker Chassis (+12 Defense, +1 Armor, +5 Piloting)
Traits/Cannot be removed, Unlimited Upgrade Slots
vs
Caeltech Light Combat Armor (+1 Armor, +12 Def)
Traits: Equippable, one Upgrade Slot (Empty)
Now for the other questions...
Some Humoids are actually originally Humans, changed around so much they can't really tell the legal difference anymore. Most Oids are 'just' machines.
Chips are physical chips. Game logic suggests they might look like floppy discs.
I've never played the RPGs (Which might explain alot), but FIOS are indeed cyberspace programs. In fact, since no created a successful Techoid, I'm still working on the cyberspace realm. News at 11.
FIOS are indeed sapient, and they will talk to you
and perhaps fall in love with you, but they have their own separate lives from the work they do for Oids. You could imagine it as your head being the place they go to work every day. They're almost always still connected to the net, though.
FIOS could hijack an OID and drive them around-they're extremely advanced, and thus come with those risks. And yes, at that point, they can choose to create a body and be considered a Techoid. Possession and Mind Control were going to be one of my higher tier Techoid powers.
You know, I think a Techoid could 'ride' as a FIO in another Oid, but it'd be pretty crowded in there...as the OP says, too much and too long and you get schizophrenic robomania as all the personalities meld together.