I speak with experience coming from the Japanese Straightening side of the coin. Definitely do a search on the forums- there are several threads about it and places it's mentioned that you may find helpful.
A few things to consider:
*The fact that you still may have to flat iron and/or blow dry with Japanese straightening. I had a slight bend to my hair still. There was no, "just blow dry with a paddle/round brush and go" straight hair. It was straighter with a slight bend, I wouldn't say there were a lot of fly aways, it just looked like a frazzled mess though, but it was bigger, if that makes sense. I began with extremely healthy hair, and the only way to get it sleek was with an iron still.
*The damage- you say you really like longer hair, but TR'ed hair WILL break off, despite how well you take care of it. It will never be at the most optimal health level as it could be as when it's natural. You may experience lots of split ends, breakage (especially where the demarcation line will be on the new growth/relaxed hair).
*Upkeep and maintenance costs and potentially having to grow it out again if you're unsatisfied at any point. Depending on your hair type, transitioning can be a real ordeal.
As far as the BKT is concerned, do your research because there's a lot to be said in terms of what risks health wise you are taking. There are tons of different brands, and if they say they are free of harmful ingredients, backtrack and do your research. There's stuff going on behind the scenes with these things that aren't always obvious, because currently (at least in the U.S.) the products used aren't being regulated.
HTH a little bit and good luck, whatever you choose