learning to FMQ, need suggestions
 

This is also the first quilt I have set on point. The quilt will be king size so I plan to quilt in 3 diagonal sections. I want to add border but am not sure how to do so. I think cutting border in 3 diagonal sections will look bad. If I add after I quilt the three sections how will I add border? Any suggestions? Thanks

By the way I have filled in the side and top triangles with the white you see in the blocks.

When I made mine, I cut out a solid color the same size as you quilt block, and then cut them in half from the right bottom corner to the top left corner. Then I sewed them together to make the quilt square all the way around, then add your borders the sizes and colors you like. I would take the three fabrics and fold them the size you want to make the border, and then you can see the way it looks before you cut the fabric. Good luck with it, I hope I explained it so you can understand what I mean.

Should I quilt the mid sections before adding the borders?

That is a good question. Unfortunately I do not have an answer for you; however, I am sure someone will come along to help you out. Your blocks are beautiful.

I would suggest making your quilt blocks or insets by doing what fellow board member suggested, that is measure the unfinished size of your blocks and cut your white fabric or whatever color you are going to use to finish rows and cut in 1/2 diagonally and add the fill in 1/2 blocks to end of each row to finish and make your quilt square, sew your rows together (however many you will quilt at a time). Finish sewing your rows of three or whatever to join - then add your borders and quilt separately. Hope this helps, late not thinking too clearly. Thank you.

That is what I thought to be the best plan. I need to decide whether to leave batting to original blocks to cover the border to be added or to plan to add the batting with the added border. What are seasoned quilter recommendations?

Sounds like you are trying to do an adaptation of the "quilt as you go" technique. I quilt on a longarm, so the tops are totally complete when I put them on my frame, so I'm not sure how to do the "QAYG", but you can google it and I'm sure there will be multiple tutorials showing you how to do it. About adding your border...I would do that before I quilted the sections since when you piece a border you do it at a 45 degree angle, not straight across, so the angle of your blocks and setting triangles will be perfect to continue the 45 degree angle. Is there a reason you are doing the quilting in three pieces? I would think it would be easier to put the whole quilt top together before quilting, even if you are squishing it through a domestic machine. Leah Day has great tutorials for quilting on a DSM on her blog.

Never did machine quilting. I'm not sure I can squeeze king size into domestic machine and manipulate the quilting.

It looks great so far.
When I decided to quilt king quilts in sections on my home machine, I found that I needed to add the border later. It turned out to be important to stop the quilting of the sections about 4-5" from the border so that I did not have a pucker problem in adding that border. By the way, your setting blocks are perfect for some fancy quilting. I'd probably do a floral pattern there, but that's just my preference.

You can go either way with the batting but my preference is adding it later so that it is not distorted.