luvmydogs,
A few thoughts from my experiences with the Ebony 5x4 non-folder, other 5x4 folders, my 5x7 non-folding Walker and lots of lenses:
Format - 5x7 viable? - Big fat YES....if you intend to primarily shoot mono, as I do. Ilford and many eastern European companies make plenty of 5x7 film. With the 5x4 reducer you have 5x4 quickload Acros (or Tmax if so inclined) for travels when loading holders is a no-no. You can also shoot sheet colour in 5x4 with ease, tho 5x7 colour is freely available in the US/Japan. You might also be able to get a Canham 6x17 back to fit.....(Spk to ebony...fits the walker 5x7). The neg IS significantly larger than 5x4. Once a 5x4 is cropped very slightly on the short axis (to un-stubby it, which I often do) it is HALF the size of 5x7. That is significant.
Lenses: As Baxter says, 5x7 lenses are larger and heavier and more expensive, but only very slightly. Take the following lenses as an example:
90mm Nikkor SW (smallest lightest 90mm f8) - 235mm circle!
110XL (OK this one is expensive, but small light brilliant etc)
120 f8 Nikkor/Schneider - Not that small but plenty available used at good prices
150 G claron (covers aparrently. I have one, but no shutter and not tested yet)
150 Sironar W (Small, compact and first rate, but pricey and rare)
180 5.6 plasmat (All manufacters have ones that cover nicely...Symmar L has 277mm!)
210 Glaron - Tiny, light, cheap, sharp, huge coverage.
210 5.6 plasmats -cheap, abundant, cover easily.
240 G claron - Ditto
300mm Nikkor M f9, Rody Geronar f9, Fuji 300 f9/8.5- Tiny, light huge coverage
400mm Schneider/Fuji...teles
450 Fuji C 12.5 .......Copal 1, 245g!!!!
As you can see there are loads of small light (some are also cheap) lenses that cover 5x7...Crumbs, the 210 G claron covers 10x8 and the 110/120s come close! I would say overall, If you think about lens chopice hard, you can do 5x7 for the same money and weight as someone who tries less hard on their 5x4 set up. Many 5x4 users use 210 plasmats at 450g. You could use a G claron at half the weight. Your 90mm Nikkor f8 or Any 90mm 4.5 is commonly used for 5x4, the 90mm being small and light even for 5x4!. Apart from your 110/120/150 focal length everything else can be cheap and small. In the 110-150 length there is a trade off. The 120s are good value but 600-700g.... The 110 is 440g but expensive......The 105 Fuji SW is bigish but resonably priced if you dont get into a bidding war!!!!The 150 G claron I am not convinced will cover well enough and the 150 Sironar W is rare and quite expensive used.
Folder Vs Non Folder - Are you going to shoot mainly short or long lenses? If you shoot at the extremes your deicsion is made. If you love ultrawides, go non-folding for greater movement, compressibility and parralellism. If you love long lenses go folder for more extension. If you shoot middling lenses scratch your head. The non-folders are much faster to set up, lighter, not that the folders take long, it is just that non-folders are almost instant!! Now for the reasons I went for the Walker:
VERY good value - A tiny fraction of the price for an Ebony 5x7 equivalent non-folder.
Poss even more rigid (more rigid than my Ebony 5x4, not that I thought this possible)- This is a tank, almost indestructable, but light at 2.7Kg
Simple and fast to set up (non-folder)
Great with short lenses (will take 72 XL on flat panel)
Will take 400 telexenar
Has reducing back available/bag bellows...usual accs
Canham 6x17 back fits perfectly and there is not a more solid platform for this back than this Walker. Fixed rear standard. Spk to owners, these are the most robust cameras about.
The Ebony non-folders have many of the same attributes above but have more movements (which I dont need). Personally I have never needed swing for landscapes or absolutely had to have rear movements.. I shoot primarily short lenses (UK...few grand vistas like USA, everything is more up close...less opportunity for long lenses from afar!!!! I decided that a non-folder helped me speed-wise in the notoriously unpredictable UK weather and made perfect sense as I knew I would be using mainly from 110mm to 210 in 5x7. I could not afford the Ebony, so the Walker was my only option. I then discovereg I lived 20 mins away from Mike Walker so dropped in...yet to be convinced of this ABS camera wizardry! That was when I discovered just how robust these cameras are and how durable. The decision was easy. They are also quite lovely in their on right
Hope this helps.
Tom