I will use my setup mainly for photography and webdesign and will be working with Photoshop, Illustrator, Dreamweaver, Indesign and Lightroom.
Can anyone help me to decide, i'm going slightly crazy!
If you asked this exact same question on a Photography website, there would be a totally different tone taken.
I am going to make a leap here to say that you are not doing the Photography and Webdesign for personal interest, so likely there is a client involved paying for work.
The side you need to look into then is not how much local storage that I have, but how am I going to backup and archive the work that I am doing. HINT: None of that is local storage. So you are already into multiple external drives with your business, so all the parts about a fusion giving you a clean desk without the next to go external is all gone out the window. YOU WILL NEED EXTERNAL for multiple drive backups, of which one of them will be kept offsite.
I have multiple NAS drives that I use with my iMac. Each of the NAS has multiple drives in either a mirror or RAID configuration so I have at least single disk failure protection (in my big NAS I have RAID6 for dual drive failure protection). All them are external drives. I have a 512SSD but that was just that I got a great deal on it through the refurb program. I would have gotten a 256SSD otherwise.
I have a 3tb Lacie Thunderbolt drive on my desk that sits behind the iMac and I use that as a scratch disk and temp work drive. it is plenty fast enough for that use for me.
I have Timemachine running on a mirrored NAS. I backup all my work daily to my backup NAS for all my local files to duplicate what is backing up on the Timemachine. I have had drives fail. It does happen and I have never lost a bit of data. I have due to my backup practices saved my own ass when I did a brutal mistake and didn't catch it for 3 days. Saved many hours of work that it would have taken to fix.
If this is a business, then look at the work flow.