Join Date: Jun 2010
Location: Jakarta, Indonesia
Welcome to the forum, Mat.
I can't advise on tank size in accordence to heaters. But in general, if you could heat it, 19ltr is enough for one betta. However, bettas might snack on the shrimps.
And as for male/female - thats personal preference. Both have similar needs, both may be equally active and aggressive. Personally, I prefer males as they are more vibrant.
I mainly use anacharis and cabomba, either anchored or left floating. They grow pretty fast and can eventually adapt to low light. You can group them in 3-5 per anchor and bunch them to create a secure hide out for the betta.
Looking forward to seeing your little buddy soon.