Yes there are other 5 gallon long tanks but fluval doesn't have one. 

Yes, they do. You can buy the heater separately. I bought one that would fit in the reservoir (a tight fit, but it fit!), but you could put it in the main part of the tanks, too.

1/8” thick glass

Depends on bio load and which type if just sponge then every 6 months if ammonia or carbon filter then monthly. I rinse my foam filters but dont clean them with every water change

Yes

white film could be a dead bacteria protein, which is normal to startup tank. Also if you are setting this near kitchen... every time you cook something with oil on a pan, oil vapor will fly around and land on the opening, which can contribute to the oily film. Aerate in the tank or the small 1.5x1.5 section where pump is located, over time film will disappear as long as no new inputs are made like previously mentioned. IF the white film you mention is more of a solid than the flowable matter, then you may have High Ca/Mg in the water you use, check the Hardness of water. If it is too hard for fishes then add Natural acidifier to see if it goes away. but my guess is on the bacterial die down, if you are trying to cycle your tank before the fishes, you need nitrogen injection to kick start the cycle. good luck.

Yes it comes with a lid.

I have 2 of these set up for Bettas and my boys seem very healthy and happy. I do a partial water change weekly and the filter is very easy to maintain. There’s plenty of room for small logs and my plants grow like crazy. I keep some snails and shrimp to take care of algae. I think these tanks are beautiful and my fish are thriving 

NO! This tank has a filter that can easily suck fish in to thier death. Buy something else for the sake of your fish.

I change 1/5th to about 1/3rd of the water every single week. Both from researching into it and personal experience I know it is extremely important not to change a lot more or too infrequently.