are the period(s) after you start T any different from the ones before starting? maybe shorter *hopeful look*?

I think it depends. For me personally it shortened it and made it much lighter. I started on patches I had one because I started on the 3rd day of shark week and haven't had any since.

I didn't have a period after starting T. I started T about 1-2 weeks before my period was due, and it just never came. Ever again. It's been almost 3 years and I definitely want a hysto because if T ran out (my area has run out of injectable before) I think I would completely lose it if my periods came back.

Unfortunately, there's no way to predict how your period will react to taking T.

Mine went the opposite direction of "short and quick" and "never having another one after the first injection". 

Mine went for nearly 3 months almost non-stop - I would bleed profusely, the heaviest I had ever experienced, and painfully for 2 full weeks - stop for about 5 days, then start another 2 weeks of bleeding and cramping.  It was horrific, but luckily, when it stopped - it didn't come back, and hasn't since (hoping that it stays that way after 2 years now).