Firstly the regency sofa. It does seem to e high quality and also very well upholstered. A very elegant piece.
The market has turned against antiques of this type but the fabric is fairly neutral and it would grace certain types of household style.
Soft furnishings are difficult to predict in auction because to get a good price requires there to be competition in the room and that is hard to predict at present with visits to auction houses by private individuals still not fully recovered.
A fairly broad estimate of £800-£1200 seems sensible.
The sideboard is not at all a fashionable item these days and yours looks to be early 20th century (or a good modern copy) hard to be certain without seeing it. Because sideboards are so very out of fashion, the good quality of the piece cannot overturn the lack of interest in such items. I think that only £100/150 is an auction guide.
The modern chair is not one that I can immediately attach a design name to. Does it have any identification marks or symbols please? The stool is a gain modern and unless attributable to a known designer is worth £30-£50.
The porcelain clock case and modern movement is a little fussy for modern taste and worth £80-£100
The kingwood table with metal (ormolu?) mounts is very French in style and being small would fit into many household situations. The quality looks good. Probably worth £200-£300.
The rather unusual 'demi-lune' cabinet is modern of course and seems to be excellent quality. It still qualifies as 'brown furniture' though and that is quite out of fashion. Its small size makes it suitable for modern homes and it is a good storage piece. I think an estimate of just under £100 is sensible.
Very difficult to assess the painting. It is very 'broad' in execution and lacking the detail associated with good painting. If it is a mid 20th century oil painting by a lesser artist then £40/50 would be reasonable.
The machine made modern rug is worth £40/50 also. Hope that all helps. These multiple item questions are unfortunately not the most popular for experts to answer - hence the delay sometimes in getting a response. Best wishes. Greg