Looks like you've thought of most things.
You didn't mention, though perhaps have it planned ..... how you plan to manage thread, notions, tools .... I'd opt for some shallow drawers with those easy slides on them, if I had my choice!

Design wall you have .... and larger is always better!

I can't say enough about the importance of good lighting, as already mentioned by others!

Have fun with the planning! :)

lots of outlets!
 

If you are having alot of builtins make sure you don't cover up needed outlets. My sewing rm is 27 x 30 and i knew my midarm was going to be near the center of the rm for ease of putting on quilts so in the ceiling I have drop down extension cords (from Sears) just like my DH has in his wood work shop. I use it for my ironing board as well. So nice, out of the way, just reach up and pull down. :)

If you are having that cutting table built you can put oodles of storage all around and under it. See my pictures on my page www.designsinthread.weebly.com You can't believe how much extra storage you can get

Were we supposed to find pictures of your cutting table and storage?
Maybe so? but I couldn't find them!

Dust- and sun-protected fabric storage. I prefer to store my fabric stored upright - like it is in my LQS. I use foam core cut to the size of the space between my shelves - others use thinner, but stiff acid-free material to wrap their fabric on. You can see all your fabric at once, and it's much easier to take it out AND to put it back. In CT, I have mine on shelves with shades that roll down from the ceiling to protect from the sun. In AZ, my stash is in a closet.

Don't forget the thread storage!

I like having a mirror so I can hold up a block or fabric combination and look at it in a mirror. It allows me to 'see' it from a distance. A hand mirror works fine if you look at a design wall using the mirror.

Increase electrical outlets!!!!!!!!!!!!!!!!!! Floor outlets where the machines are going is really nice. Task lighting. If you have light coming from the left to right over the sewing machine needle you will have less shadowing. How about a TV/Music? I saw a cutting table that had a long slot in it that was for sliding scraps/waste into. How about a sitting chair and foot rest? My design wall would be more than one that would slide behind each other like a three panel closet door. I am happy for you and hope you enjoy your sewing cave! I just got a 4 tier revolving shoe rack that I am planning on clipping patterns too, rulers, fabric and notions. I area is at the end of a family room and my husband says it is creaping out of my designated area!

You mentioned that there will be a lot of built ins ... and then it'll be too late for changes!

Not really ... built ins can be made so that they are not permanent, yet are solid for your use and seem permanet.

Then when/if the time comes and you want/need to rearrange them, you have the potential to easily move them. And once again, they become "permanent" .... til the next need arises!

You may think now, it's the long term plan ... as a new quilter, you'd be best to allow for flexibility for the future, whether for quilting, or some other avenue your interests take you!

How do you buy your batting? How will you store it? I buy mine by the roll, so I had hubby make me a giant papertowel holder style thing for my closet to hold the batting. Lots of outlets, lights, table space to spread out on (nothing worse that moving things over and over because you don't have enough room), large ironing surface, lots of drawers for storage, peg board, entertainment center (TV and/or radio).

Can anything your planning do double duty? For example, my fabric is all stored in wardrobes that I bought at True Value Hardware. My hubby covered the doors with homosote board and batting to make my design wall. I have a huge design wall without taking up extra wall space just for the design wall.