It looks like a great tomato. Will you be able to plant it outside soon when the weather warms up? If so, I wouldn't prune anything as it will do well outside. If you are keeping it inside and worried that it will take over the room and be difficult to contain, then I would prune to one stem and remove all the suckers.

How big is the pot? Indeterminate tomatoes can grow huge - 6-8' tall or taller and that means they develop a huge root system as well. Most tomato growers who grow in containers use 10-15 gallon sized ones at a minimum and typically even largerones. I personally use 20G pots and a single plant will fill that by the end of the season.

And get it outside as soon as you possibly can!! It is not getting enough light to develop properly indoors, even in that window.