It's hard to tell what exact year this is, but it likely late 1790s or early 1800s. The standup collar of the uniforms came in the late 1780s but was standard by then. With the picture in black and white, it's hard to tell the color of the collar, cuff, and lapel, but royal blue is found on almost all general coats in the era. However, generals and other officers wore a scarlet red of the finest wool broadcloth available to them. Can see an example here. Military records described it as superfine cloth. It is smooth and softer to the touch than a rough quality of cloth that enlisted soldiers had.

The ornaments do mean things. The stars on his leftside are not denotations of rank, but of his knighthood - Order of the Bath. I suppose it does mean what rank he is in society and politics though. Officers of all ranks had metallic lace on their collars, lapels, cuffs, and for generals on the sleeve. For the most part, they are gold, but some regiments did use silver for their junior officers. The picture you linked did not show his sleeves but this one does, and with the six chevrons paired in threes shows his rank as lieutenant general. The linked picture also has him with two epaulettes as well instead of the one with the braided cords you linked. The two epaulettes signified a colonel of a regiment at one point in the eighteenth century, which I gather is what he is also showing here. I want to add that commissioned officer ranks in the eighteenth century and at least the first half of the nineteenth century differed from today's military ranks with the fact that one can be one rank in the army and another in the regiment. For example, Cradock was a lieutenant general in the army, but the colonel of a regiment. It could happen to those lower than generals as well. John Andre, the famous spy in the American War of Independence, had a rank of major in the army, but captain in the 54th regiment.

His Crimson sash around his waist is part of officer ranks as well. For the most part British officers wore them around their waist, the only exclusion for that would be the officers serving in Highland regiments. Just one of the few distinctions. His shoulder sash or riband is also a symbol of the Order of Bath. Robert Murray Keith's portrait might give some insight on how it looks, but in a uniform of an earlier era (thirty years or so prior).

Hope that helps some. Uniforms change a lot between eras and generals have some distinctions with each other.