Welcome to the forum! Migi is a beaury--Love the pattern on her back...so artistic! Your set up looks great, and the reptisuns are good UVB sources.I use a reptisun 24" tube light for desert reptiles, and have been quite satisfied. As to size, I have a 40 gallon reptile tank--it is longer and wider than a 40 gal fish tank, and the glass is less reflective. I started out with a fishtank, but my boy saw his reflection in it and was constantly agitated, bearding and glass surfing.
The 40 would be too small for my boy (he is big! a full 24 inches and still growing!) But I am always home, and Dezi gets lots of time out of his viv, so he gets his exercise and seems happy and healthy. Also, we take long trips in an RV, and Dezi gets to be a free roaming Beardie in the RV. He loves that. He has a viv in the RV almost identical to his one at home, but seldom uses it. He has a ledge behind the RV sofa next to a window, with his lamps set up there, so that is his usual place in the daytime. I had to remove all the pretty decorative items from his vivs, to give him more space, so I would like to get him into a bigger home viv that I could decorate, but have space issues.
So, the best size of your Migi's viv will depend on your available space, finances, his activity level, size, time outside her viv, etc. Does that help at all? I think maybe it just added more complications to your question--sorry! ??.
tameness and docility seem to be a product of several factors: frequent handling is most important. Dez spends several hours on/with me every day. I got him at around 8 weeks, and began handling him immediately. I socialized him by having visitors hold him, and taking him for car rides and visits to pet stores. He is totally relaxed in any environment, as long as he can see me. Another factor of tameness is the individual personality of the Beardie...each one is different. Some have high energy levels, while others are just naturally more laid back and social. Age also makes a big difference. At around six months (puberty), they tend to settle down and become more confident. The older they get, the more relaxed and confident they become. Dezi is three years, and totally laid back.
Everything about these remarkable creatures is quite individual. They are such complex, intelligent, emotional beings! I would never have believed it, before I became Dezis willing slave. He has sucha huge range of emotion, and as we got to know one another, I learned his body language and facial expressions, so now we communicate as well as any pet I have had. Our bond is deep, and beautiful. You will have this with your lovely Migi, too! Welcome to the wonderful world of Bearded dragons.
Here is Dezi, showing his laid back attitude...