You can easily get bogged down with all the different numbers and specifications - I remember buying my first scope and it's a bit overwhelming. You've picked some great scopes there, any of them would do the job, but which would do it best? Well, that comes down to what you want to get out of it.
Given your enthusiasm and the examples given I think the Esprit 100 won't have enough focal length for you. My old ED102 had a focal length of 714mm and for me it wasn't quite enough - sure, you could fit the majority of eta Carina in but other nebula appeared a bit small for my liking. At 550mm I think you will quickly outgrow the Esprit 100. The 120 at 840mm is a much better choice I think.
Yes, you will have to image for longer with the Esprit 120 at f/7 - but really so what? If it's going to give you the kind of photos you want then that's what matters. I understand you're concerned about SNR but again, that's just one of the things you'll have to account for to get the photos you want. With proper cooling the noise can be kept under control quite well.
One other thing - this hobby takes an incredible amount of patience. Those amazing images you see - you probably won't be able to get that kind of quality until you have a lot of practice. I too am chasing the ability to take those breathtaking shots, be patient with it otherwise it's easy to get frustrated along the way
