We have a 5 metre set of aluminium bifolds. They are lovely, they cost £7.5k with installation and comprise five doors in total.
There were lots of options with regard to how they opened. Ours have the main handle at one end and all fold back to the right, however, 5 metres of door is very heavy and in hindsight I think opening in the middle and folding half and half (half to each end) might have been preferable due to weight as it's a lot of load on the mechanism. We haven't had them open much in the year they've been installed (due to poor weather all summer) but next summer I think we'll get a lump of wood to rest them on when they are open.
You need to think about which way they will fold and also whether the open doors protrude into the room or into the garden. Ours protrude into the garden because they would get in the way of a doorway if they were protruding into the house, however, they open onto a wide path rather than a patio, which is the main reason they fold one way (if they folded both ways, you would have to step around them twice if that makes sense).
With regard to window coverings, our house is not overlooked so we decided to give it time and see how we got on without blinds. It's actually fine but I did have somebody quote for cartridge binds (remote controlled - five individually controllable blinds concealed in cartridges at the top of the window recess) and this came out at £1,500. You can have glass installed with blinds inside the cavity - I figured this was just something else that could go wrong but other people who have them will prob disagree.
There are two main drawbacks to my bifolds. (1) they are inevitably more draughty than a wall/windows would have been, which means the corner of the room which houses the dining table can become quite cold at times - I only really notice it if the temp outside dips below 5 degrees. (2) The full-length view of our lawn has not always been welcome during a very wet summer when it has been impossible at times to get out and maintain it. It does provide a lovely backdrop when the lawn has been mowed, but at other times it has looked an absolute mess and I'd have preferred not to have it in my face.
They are great for parties!