Although I have seen quilts with borders as small as 1/8", the narrowest border I do is 1/2" finished (cut at 1") anything smaller and I use a flange. In both cases, you need to cut the pieces accurately and maintain a consistent seam, because of the small width.
It sounds like you are concerned that the quilt size will deviate a small amount depending on the technique you choose. Unless you are making this to fit a specific place, like a window opening, the size difference you are talking about doesn't matter. If it needs to be a specific size, you can reduce the final border to make up the difference. When it comes to border widths, many folks just lay the fabrics out and move them back & forth until they get a grouping that is pleasing to their eye.
Same with reducing the gold border to 3/4". You probably will not notice.
You can quilt over the flange, just make sure you don't flip it. The unquilted spots in the folded edge will just add dimension.
If you are truly concerned about quilting with the flange, then I would just go with the narrow pieced border.