Re: hub thingy
you have the locating pin one side and a small bolt the opposite side of the disc.
They help align the wheel (usefull as they can be a pain).
They also hold the disk onto the hub.....this isn't important when running the car, as it will be sandwiched by the wheel bolts between the hub and wheel.
If you run without both of them though, as mentioned, the spacer, if its generic, will keep falling off, and refitting the wheel will be a royal pita. It also leaves room for the spaver to be secured off centre, introducing unbalanced wheels. If the disc isn't corroded onto the hub, if tyou ever remove the calliper, you may find your disc crashing onto the floor/yourfoot.
I'd drill small holes to fit both the alignment peg and the bolt.
What size are they though? Hubcentric are better, adn FIAT do a nice 10mm set for not much ££.
Cheers,
KRistian