First, what do you need light for? Do you do paperwork? Is your desk in your window? You'll be getting afternoon sun. I'm recommending LED lighting to people, but Fred says it has a way to go in brightness and affordability. I recommend sky tubes to homeowners. I've had 2 in one of my houses.

What Dr Retro says above. The short answer is it would be rare to use the same paint throughout as you’re dealing with a number of different surfaces & end uses. Paints are designed for each specific application. Ceilings: use matt ceiling white, or if you want a coloured ceiling, tinted ceiling white. If you‘re doing a ceiling feature a satin finish could be used as long as the ceiling’s in good condition. If the ceiling’s in average condition some professional painters use an oil based undercoat instead of water based ceiling white. Walls: use water based satin finish, some brands call it low sheen. Walls in wet areas: depends how good your ventilation systems are in these rooms, sometimes worthwhile to use the lowest level of gloss paint (water based semi gloss) but as Dr Retro said above the higher the level of gloss the better condition your walls need to be in. If you have areas of new plasterwork, or cracks & holes that have been filled, apply a sealer binder over these areas before top coats, or the plaster patching will show through your top coats as it takes up the paint differently from the non plastered surfaces. On new woodwork use an undercoat then your preferred gloss level ie. semi gloss, gloss, or high gloss only where the surfaces are perfect (very rare). Some paints are promoted as primer/undercoat/topcoat all in one. I’ve found the finish is better using undercoat, then top coat, but that’s my personal preference. On existing/already painted woodwork: use undercoat on any filling/patching, then same topcoats as for new woodwork. If the existing colour is dark & you’re going to a light colour undercoat is recommended, or many top coats will be required to cover the dark original colour. Bare wood with a high tannin content is best sealed to avoid tannins bleeding through to your topcoats.

To me , I'd want to know the style and era of the house , and the look of the other rooms , and even the size of the room . On it's own , with that art , and white walls and timber floor , I'd say do a white leather suite ( or 5 or 6 matching white leather chairs ) and a large screen TV on another wall , and a large coffee table in either white gloss , or black frame and smoke glass top . And then set it off with 3 or 4 green leafy potplants ( all different plants and different heights ) in pots in similar blue and green and mustard hues as the art . Any windows do in light wooden ventians ( white slats would be overkill without seeing the room IMO ) or black as a contrast . Add a mustard or jute rug . BUT that may not suit the rest of the house , or the size or shape of the room .

I'd do it the same off-white as your upstairs , even if you have to paint over your stratco . BUT of more concern to me ( visually ) is the galvanised beams -- surely you'd paint them the same as your gutters and trim , so it looks like your house is designed as an integrated 2 storied place , rather than simply a house slapped on some beams , that you park your cars under ?