@macvisual - some s/h retailers do offer credit facilities on gear, Wilkinsons do on items over £500 - they have no bodies and only a couple of lenses available.
The 50SII plus 'kit' 35-70 is on £700 off promotion at the moment (total £3199)- and is available on Finance, from many major sellers, Clifton Cameras do have a 12 month interest free option and Wilkinsons have a 12 month Buy Now pay later option on this package (if you don't pay then it goes onto a 36 month finance deal). I have used interest free finance from both in past (Canon R6 for my step-daughter from Clifton and GF100-200 from Wilkinsons) and it worked seamlessly, though in both cases it was that I'd rather keep the money in my account than theirs, so just opted to spread payments, I didn't 'need' to
You have to be sure about the GFX, its a considered 'spend', the bodies are quite bulky (and slow, though nipper than your X-Pro/X-E1, think X-T1 like performance and you wont be far wrong) and there is a limited range of lenses (nothing particularly fast and nothing particularly long). If your photography fits the Digital MF criteria, then IMO there is nothing quite like it, and the images/files still amaze me 3 years in. I'm fortunate that I have all the lenses that I need at the moment, I even managed to turn down a GF23mm and GF110mm that a friend was selling (cheap) as they are lenses that I 'want' not 'need'!!! Less choice is better for my photography, my bank balance and my bag weight. In fact I would be happy with a GFX50S + GF45mm - a supersized X100.
Think about it carefully, try and borrow one from a dealer, perhaps Ffordes may help here, you do really need to know that its right for you before buying, and doubly so if you are going to use any form of finance.