I'd sew them all together first as well. As someone else mentioned, not only will you need to add longer lengths for each successive border, but you will need to have the whole set overall longer as well if you're planning to miter the corners. It's far easier to miter with all borders sew together THEN do the mitered corners.

Why not split the difference? The wide borders shouldn't be much problem but the 1 inch ones might be tricky. If you sewed the 1" black to the 6" gray and attached those together you don't need much extra fabric, just treat it like a 7" border. Then do the same with the black and red. You won't waste much extra fabric and won't have to work with the 1" borders separately.

OK, do you want mitered or not? If you want straight borders do you want horizontal or vertical? Would you accept a cornerstone block at each corner - this could be a part of your quilt design highlighted or not? What effect do you want overall?

I do my mitered borders as one piece as it is much easier to do. I can fold one edge back to line up the different borders, iron, and pin as needed. Because I start with what I can see the borders work. If you felt better you could glue baste the underturned part and baste the seam first to check it out.

i would add them as a group and then you only have to miter each corner one time.

If you are unsure of the miter do a prctice piece on a 18 or 20 inch square of scrap material. Try doing miters around it with varying widths of strips. They aren't really hard to do. It is a matter of learning. So do some trials to learn first then go to your project.

peace

So true about wavy borders. Found that out the hard way. I would make the borders as a strip set then miter. I am working on a quilt now with a 5 piece border & don't have enough fabric to miter. I am doing a lot of measuring & pinning to hopefully avoid waves!