Got it in one, glass/greenhouses rely on the sun for heat, and the cost of the additional heat required during cool periods would probably exceed the amount you'd save but the solar heating during the day. Better off in an insulated room IMO, and heat the room with a heat pump to help maintain the temperature. Could possibly do a tropical pond in a glasshouse over summer, but would have to be wary of over-heating, not hard for a glass house to hit 40-50C on a sunny day if not well ventilated.
Yeah ultima would be a good option for mega filtration, not cheap but tidy, efficient and awesome.
Heating cable is another option for heating large tanks. I have a friend with a 3000L+ DIY tank (yes it has a window) heated with heating cable underneath the tank and it works really well.
The most realistic option by far is to move to Malaysia. When it comes to tropical ponds its pretty hard to top this guy: http://www.monsterfishkeepers.com/forum ... p?t=341560
Check out some of his threads, 13000g, 40" royal clown knives, aros, catfish etc. Madness!!