It's been a long time since I grew this, so I did a little research to confirm my memories. You're not starting out with the easiest begonia to grow! Reigers are generally grown as 'throw-away' plants, a practise I rather deplore, tho' maybe if I were trying to make a living selling plants to the public I'd feel differently. The main things is they need to go dormant for awhile each year. Also I think yours is probably a little over-potted. What I read, and I think what I did, was to cut them down to an inch or so and keep them cool and on the dry side for a period. Then when you see them starting to grow give them good light and start watering and fertilizing. Definitely do-able, definitely more bother than most begonias. So far you've done quite well!

Thank you so much for your input. I'm going to try trimming it down and see what happens. I won't be so bummed if it dies then, since it was meant to be a toss em' kinda thing.