I'm going to be traveling from Bruges to Brussels as well as day trips from the latter to Antwerp and Ghent. I'd prefer not to tie myself down to much with times. Is it hard to get same day tickets at the train station to travel between cities or should I buy in advance?
No problem at all; those trains are all frequent (e.g. there are 99 trains a day covering the one hour ride from Bruges to Brussels) short distance commuter regional trains, you just show up buy your ticket and sit where ever. they are fixed price and don't sell out. The tickets are not expensive so I'd buy a ticket to sit in the first class area of those trains especially on the Bruges to Brussels route since they can get crowded if you travel during morning or evening rush hours. You can buy them in advance also since the ticket is not for any specific train or time. The ticket is good for any train for the day you purchase it for.
No problem. Trains are frequently with lots of seats.
and it is even easier and cheaper if you are senior citizens - day trip tickets on Belgian trains for seniors are really really cheap.
The app for the train company is easy to use and worth having. You can just buy your tickets using it