On the question of letting a room, Owners Corps can’t pass by-laws that a) conflict with superior laws and b) interfere with your “dealing” with your lot. This means they can ban short-stay lets of entire apartments (if the building’s zoning is residential only) but they can’t tell you what to do with rooms in your apartment (although new laws will allow OCs to set occupancy limits, provided the limit is no lower than two adults per bedroom).
So, in the first instance, point your committee in the direction of clause 49.1 of the strata Act.
49 Restrictions on by-laws
(1) By-law cannot prevent dealing relating to lot
No by-law is capable of operating to prohibit or restrict the devolution of a lot or a transfer, lease, mortgage, or other dealing relating to a lot.
On the second point, take some pictures of committee members’ and other cars parked on common property then send them a polite letter inviting them to take you to Fair Trading mediation and then to NCAT so that you can all amicably resolve the issue by getting orders that NO owner can park on common property, including the owners of the following cars. Otherwise, they should stop harrassing you.
Re the bollards, send a letter to the committee pointing out that the bollards have rendered the parking garage area unfit for purpose and they need to remedy this under their duty to maintain and repair common property.