Lookin forward to seein how it goes this winter. I am planning a stock tank pond for my Oscar. I am a bit North of you so he may just go in for the summers.
Broke out the bigger pump. I'm only going to run it every other day over night, considering its a utility pump and sucks up electricity like crazy. Hopefully it clears up a little. Right now visibility is about 1-1.5ft
Those 2-3 months are gonna be harsh if you're not planning on using electrical heating .its pretty expensive but a huge investment! Try purchasing solar panels for electricity to run your pond .that or you might wanna bring all your fishes inside during winter cause I don't think the green house thing is gonna work for 2 or 3 months.rather be safe than sorry bro! Goodluck!
It might be to late but you should use insulation between the pond liner and the ground. For the winter if you set up a camping or party tent with walls it will insulate much of the heat. Or even a cheap wood structure will help with the heat, you can then insulate it cheaply with newspaper and cardboard. Even coat it with millard which is wrapping paper an the survival blankets. Even investing in a cheap structure now will save you money in the long run.
you said that solar heating doesn't work in the winter time because the sun, not so sure about that. after all solar is year round. ill post a few videos of passive solar water heating idea, and you can PM me if you have any question. these will work during the day light keeping in mind of a south facing design. that way you will only have to keep in mind the heating for night time hopefully. i have family in the solar industry so let me know if you have question.