Firstly, apologies, I have only read your posts, as I don't have time to read the entire thread.
From your OP, it sounds like you are largely disenchanted with bf, rather than actively disliking the actual process of having DD at your breast? It frustrates you that you can't judge the quantity your dd takes, and you're upset that you don't find it enjoyable. To me, it sounds like you need to accept the limitations of bf and set yourself a 'deadline' for stopping or continuing (a week/month) - then if you still feel this way you can move on to ff/mix feeding without beating yourself up about 'giving it another week'. You've done well to carry on for 6 weeks as it is. 
I didn't enjoy bf for the first 4/5 months (had almost every problem in the book), and didn't find it a remotely bonding experience, but it worked out in the end for us, DS is nearly 14mo and still bf.
A friend of mine had no problems at all bf, but simply found the process icky, hated every second, and practically danced down the street when she gave up after a few months - it's such a personal experience, we're all so different! Anyone who tries to lay down the law to you about bf/ff can sod right off - your baby, your boobs, your mental health.
My DS put on weight slowly too - but I was told that this wasn't a problem as long as he continued to do so consistently. Some kids are always going to be at the lower end of the centiles, someone has to be after all! It doesn't always signify a problem.
Let-down while pumping is never as strong as while baby is feeding so you often get less than baby would, and you may not have a strong let-down anyway - my HV told me I have "extremely efficient nipple sphincters"
!! I never sprayed, barely leaked after the first couple of months, and never got much out while pumping - meh.
I'd just suggest trying to accept/relax about the bfing and going with the flow for another week or two, you sound like you're putting a lot of pressure on yourself, six weeks is still early days in my book! :)
At the end of the day tho, your DD will be fine whatever method she's fed by, ff babies grow up just as big and strong as bf babies!
Sorry for looooong post...