Roman Religion and the Greek religion

[David19]

After reading through the other thread about Roman reconstructionism (i think it's just a couple of posts down below this one), i was wondering, what's the difference between the Hellenic religion and the Roman religion, i've seen people say that the Roman gods are just Greek deities with different names, but i've also read some things that seem to say the Roman deities were different to the Greek deities (like in personality wise, etc), but how else do they differ, and what other supernatural beings are part of the Roman religion (e.g. i know there's the Genius Loci, but what else).

And, just one final question, with Roman reconstructionism, do you know if you can practice more than one religion or worship different deities (like didn't the Ancient Roman's worship the official gods of Rome, but then could basically worship whoever they wanted, like Isis, Mithras, Jesus (wasn't Christianity a mystery religion before it became 'official'), other deities of different lands, etc.

Thanks for any help you can give me :).