You might try 4'x6', landscape format. We typically start by centering the object around 5' above the floor. Might work better a little higher but you can try it out with tape.

Perhaps, not strictly canopy style would work better. Qasair can do custom design, if there is not thing that would fit your need already on the market.

Good morning! I love love love your ceiling! As others have asked - is it something that repeats through the house? I would 100% keep them - the key is to work with them not fight against them. I would also replace the light fitting - look at having recess lights installed. There are a number of things that you can do when you have such a prominent feature such as this in a room - you either choose to work with it and 'calm' it down into the space - such as painting the ceiling and the walls in the same colour - or you say - to hell with it and make it the hero of the room. I have seen some stunning ceilings where the walls have been painted in a 'white' and the ceiling painted in a strong colour such as navy which then ties into accents in the room. It would obviously depend on your personal style. Good luck!

I'd make sure I had probably 3 'zones' or options . It is just crying out for a big industrial style centrepiece on 3 or 4 heavy chains , maybe even with 15 or 20 candles . Just as I'm writing this , I'm even wondering how difficult it would be to get 15 shorter stubbier candles and drill out the middles , and thread a cheap 12 volt LED through each one ? The local electrical supplier charges something like $12 for 10 -- you'd have to wire them , but its low voltage so a soldering iron and heatshrink tubing would do wonders . look way more authentic than those cheesy ones with flickering 240 volt bulbs and fake melted wax on shiny plastic bases ! Anyway , that would be my centrepiece , even if you had to use a transformer etc -- drop it to the ceiling line height . Then I'd do a seperate zone -- probably single LED spotlights ( prob in black ) . at least one each beam , some pointing up , some across to the other 'slope' , but also some pointing downwards , because you'll need to look for dropped coins or handkerchiefs or phone chargers every now and then haha . And the 3rd zone would be wall uplights and downlights , because I can almost guarantee there will be times you want light , but you don't want or need to emphasis the height . If its not too late , I'd have them maybe 1.5mtrs from the floor , and the covers in an aged copper or similar panels , and that would match the style of the centrepiece light too . I'd have the spotlights a completely seperate style though -- more modern and plainer , but not ultra-modern , if that makes sense .