No worries! It is a bit of an odd job to find out information for, as its pretty specialist in terms of retail..
1-In terms of portfolio, it depends if you want VM or Creative. For VM, examples of merchandising you've done would be good, as would anything that shows off any business-type skills, as VM is not just making the clothes look good on display, but using and analysing figures/sales reports, and acting on them to further drive sales. For Creative, anything art/fashion based you may having done, whether it be styling/illustration/installation. Anything that shows some fashion/design awareness. A current trend mood board is always good too, show you know what you are on about!
2-It's actually easier to get into Creative and then work towards VM. VM is held much higher than Creative, just because as I mentioned above, it's not just making the clothes look nice instore, but it is showing business/commercial skills, looking at and being able to use sales/stock figures in order to further drive sales, as well as being creative in the way in which the clothes are displayed. If you are established in VM, you could go anywhere and do either VM or Creative, but the same cannot be said if you are established in just Creative. It's easy enough though to go between the 2.. I work for Topman, not Topshop at Westfield, and unlike Topshop, we don't split the two, so we do both VM and Creative.
3- Requirements for VM is an odd one... You have to be both creative and fashion minded, as well as having a good business and commercial mind. Good fashion knowlege is essential though when merchandising, to create the right mood/trend with the outfir builds you make. A good work ethic is a must, as are good communication skills, because you not only have to communicate with your VM Manager, but head office VM teams, as well as shop floor teams/shop floor management, and stockroom teams. In terms of qualifications, it's again an odd one, as it's a very specific skill. Most VMs (or atleast VMs for Topshop/Topman in high profile stores) have some form of fashion/arts degree, but it's really not something that is needed.
4- At Westfield, I do both, because as I explainded, Topman don't split it the same way Topshop do. Good for me though, because I enjoy doing both!
5-I work full time, which is 37.5 hours a week, and all VMs work 7am-4pm. Sounds early, but it means that you have a few hours before the store opens to get major things done.. It's so nice as well to travel to and from work when the tube is not rammed, and you get more of an evening. You get used to the earlier start, and now I would really hate to work any other hours. We have to work the odd over night shift too for major moves/set ups, but they're really not too often. In terms of pay, you'd be on about the same. As it's more of a specialist role, the pay is better than normal sales floor staff (or it is atleast for TS/TM.)
My gf LOVES circus! The team there are all really nice/very good at their job. Circus is getting a £16million refit over the summer too, so they are all doing loads of work for that at the moment, helping design the new store. I've seen some plans, and it's going to be AMAZING! Pretty good time to get onboard there in terms of VM, because after the refit, the profile of the store/the VM there is going to go through the roof. In terms of applying, it's be near-impossible to talk to the VM Manager. I've popped in to find people for work related things, and it's taken an age to get to them, because of the size, and they were expecting me! Easiest thing to do would be to call the store and press the option to be put through to HR, or apply on their website. There is a link at the bottom, and you just choose the area you're interested in, answer some questions, and submit your CV.
I was talking to my gf about the RA, and someone on her team did the year long VM course there. He had no previous VM experience, and said it was really good, because he got to learn everything from scratch, did placements in head office/met the right people, and then secured a circus job, at a slightly higher wage! Worth looking into if applying doesn't work out and you're really serious about the career change.
Let me know how it all goes, and just ask if you have any furher questions!