Depends on what you are planning to do with the room whether to paint or not, both mantels are missing their inserts. The first photo does look like it's two pieces, the top is Art Nouvea , the second timber mantel looks Art Decco. For me the first photo with fire place I would look into a gas insert to fit, not sure whats on offer, but similar size as how to girl, you can get plain metal fireplace inserts with out tiles. You could use either mantels but I think I'd find another use for the separate mirror, perhaps over a side board cheers

if you decide you prefer the square set wood burner a metal fabricator can make a steel frame to insert inside the curve to enclose the wood burner and seal off the chimney but you should really discuss options with the wood burner installer before you buy any heater and make sure that the chimney will be safe and functional...also good opportunity to have the chimney cleaned to ensure there are no collections of soot, dead birds and other debris and the chimney should be checked all the way up to ensure that the brickwork is secure and there's a functional chimney cover to suit your intended insert...the wood burner suppliers should be able to recommend suitable tradespeople to provide all these services

A lot depends on the size of your TV and the size of your fireplace insert. If you have a clever cabinet designer than an adjacent arrangement always looks good, but you have to know what you are working with. Check out Sculpt fireplaces for some freat in-built options. https://sculptfireplaces.com.au/collection-category/contemporary-inbuilt-fireplaces/ Best of luck with your research, Dr Retro of Dr Retro House Calls

which size fireplace you choose will need to be decided by the available fireplaces to suit your needs (ie heating capacity, fuel, location of flue, overhead beams etc) so i'd start with the fireplace insert and then work all the other details from that..but, you should add scale sized furniture and suitable walking paths to the room so that the seating is angled to suit the view, the tv and the fire and you might find that the alcove with the bulkhead could be a better location for the TV and/or fireplace and storage wall