I would recommend a bigger than 10g tank for beginning sw
. BUT if thats totally not possible then you could get some nano fish, I'd say two and some shrimp and inverts. I'd stay away from the starfish, they can be a challenging to care for and the tank would be kinda small.
As far as cool/cold water fish, I know they have them but havent tried to keep any yet.
Theres a sticky on this forum for equipment needed,
Stock list and tips for maintaining your SW tank.
You wouldnt need a skimmer and a hob
filter would be fine, such as an aquaclear 30 for instance.