plastic is fine and the same one is on ebay for £30. for like a tenner or something. A re-purposed water carrier or something like that, the ones you see in water dispensers... but i think they are only 18l.
I would say it won't carb if it's been in to 17 days. It needs about a day after it's finished fermenting to clear some of the way. If in doubt just straight in the bottle with priming sugar. If sediment is a concern just leave it a month to go solid.
I say this as I have done a few and my...
I would have to measure my internal dimensions as they are all built for round tuns.. mines oblong and big. On the face of it i would need the biggest bag @ £50!
i use a 1litre jug and dont find it anything like quick or handy.. scoop, walk to bin, empty.. 20 jugs later I'm done.
lifting a bag once and taking to the bin sounds much easier..
now i think on... if i had a smaller coolbox that I could easily pick up with 10kg of wet grain (13kg?) the braid would be cheap n easy. My coolbox is massive and awkward to pick up empty.. never mind full of wet grain. I am thinking the bag is going to be a good solution.