Toilets, Sinks, Showers, Tubs and Disposals - Low Water Pressure in Tub/Shower

There was recently a water main break in the water line that feeds my condominium unit. Te main was repaired however, since, the water pressure in my tub/shower is low and my toilet either does not fill up or overflows, not sure if the toilet issue is related or just a coincidence. Any help on what the problem and solution to the problem would be great!

No such animal as "coincidence".... When the main broke and was repaired, it's more than likely that a lot of debris ended up inside the pipes and, therefore, ended up in your shower heads, aerators, and toilet fill valves - which can cause the symptoms you describe.... Take them apart, flush them out, run water through the pipes thoroughly before re-attaching the items....

How would I go about running water through the pipes? Take them apart and dump water in them? Should I use something high pressure? Is this a job you can do yourself or is it better to call a plumber?

Remove the aerators from all the sink faucets/kitchen and bathroom.... take them apart (remember how they go back together) and simply turn on both your hot and cold water supplies for a decent amount of time (considering what you had done, I'd let them run for at least 5 minutes or so.

Remove the shower head and do the same in the shower. Backflushing the shower head itself is a problem.... don't know how you would do that - though, were it me, I'd take a water hose and blast water "backwards" through those fixtures.

Study your toilet valving... it may be able to be taken apart and flushed - only examination will determine how to do so... again, remember how you took it apart so you can put it back together again... and turn off the water supply before you start unscrewing the housing...