And if you're capturing pictures on a medium with a narrow dynamic range (colour transparency film, DPP), you'll probably need some ND graduated filters too. In fact, I would favour them over a lupe, since I can still see clearly enough but can't get away without the filters. And if you can't afford a lupe, an old enlarging lens does the trick. Apart from that, Joanna is right: nothing like practicing to know what you really need.
I have taken plenty of pics without a fresnel and my pics have not suffered too badly. In fact, I must say I don't find the Sinar fresnel very easy to use. The main reason for a fresnel is to make your life easier with wide angle lenses (f less than 100mm). Strangely, I find the Sinar fresnel easiest to use at the longer lengths (f above 200mm). Which tells me it's not doing a great job. I suspect it's because the screen is not flush against the glass.
As for the GAS theory: the great thing with Sinar, and the reason I landed there, is that all these accessories
are available and give me the flexibility for me to develop my craft how I want. Not all are necessary and it is a matter of choosing what's best for one's practice. With a single camera, I can shoot 5X7, 5x4 and 6x17 - the latter with a 90mm lens fitted to a standard plate, without having to put the front standard through a yoga session either. I can shoot anything from 50mm to 750mm on flat panels. I can use old barrel lenses thanks to the Sinar shutter. Can any other camera do all that? Naturally I don't carry all that with me at all times (shame about the weight!), but I have the choice of which camera to shoot with. The ratio of choice to financial outlay is very attractive. Ignoring the lenses but including the 6x17 back, the camera cost little more than a grand and delivers far more than a TK45 or an Ebony in that price bracket. Horses for courses. I may be gassy but I am not boring.
Regards,
Charles