1. Has anyone used linelocs and rope in place of buckles and webbing for shoulder strap tensions? Whats the weight compacity, pack load wise for this kind of setup? Any durability issues for the linelocks?
Using cord instead of webbing increases the chances of its getting tangled on any number of things it comes in contact with. The webbing also will be much less abrasive if it rubs against you or your clothing, and is better at keeping the straps from twisting. When you are putting on and taking off the pack, resting your hand below the pack straps, wrestling with the pack when fording a steam, falling, sliding in the snow, or any other situation where you end up grabbing the pack by the cords, they could become quite painful and/or annoying compared to webbing.
But if you are shaving grams, a lineloc setup would be much lighter as you imply, and spectra cord is plenty strong. Don't know if it is as durable as quality nylon webbing that lasts many decades. As for the linelocs, however, just looking at and comparing the sizes of the components of a 3/4" acetal plastic ladderlock buckle vs. an acetal lineloc, the buckle has to be quite a bit stronger, and spreads the force of the web under tension over a wider area. But if you are making an ultralight pack for carrying only in the under 20 lb. range, maybe that would not be important.
I carry in the 20-25 lb. range when loaded with a full week's food and my camp chair; so want something dependable like buckles, and prefer the webbing for the reasons mentioned above.
2. I am using silnylon, heavy duty mesh and dyneema x. What is the correct method for sewing all three together? Im sure one way or another is better for the longevity of the 1.1sil.
The 1.1 oz nylon with a sil coating will weigh 1.3-1.5 oz per sq yd.
While the coating adds some resistance from unravelling to the fabric edges, the silicone does less well at this than PU. Consider using GE silicone glue (not sealant) to fold over and bond the edges of the fabric before sewing. This will greatly decrease the chances of unravelling, and also allow you to use greater thread tension, tightening the seam without puckering the fabric. I use a small hand roller, and first crease the folded edges with an iron, a risky process because it can greatly weaken the fabric, especially if the iron touches more than just the crease, or is too hot. But for me it beats having to clamp and dry the entire length of each edge.
Not sure about "dynema x," but many of the meshes, like the one called "leno" by some of the vendors, easily unravel. (There is a heavier, coated leno also, but if you are shaving grams, doubt you are using that.) The mesh probably can't be bonded at the edges like sil, but you can still fold the edges over and hem it with a row of light stitching. The dyneema will probably bond with Elmer's or Lepage's urethane glue, but haven't tried it. Buy urethane glue only in small quantities, because it cures rapidly in the container.
True lap felled seams are nice, but very difficult for a nonprofessional. There is the faux lap fell seam, which is just two pieces sewn together near their edges, with one wider edge folded over the other, laid against the material, and resewn with a second seam. This also traps the raw edges inside the seam, but is not as water resistant as the true lap fell seam, because the needle holes in one of the seams are not backed up by additional layers of fabric.
Consider one-fold hems on all the fabric edges, bonding the hem where possible and stitching where not, then pinning the edges together so that the raw edges face each other with maybe a 3/8" overlap. Then stitch with two rows of stitching as you would a lap fell seam. The raw edges will be concealed, and the bonding will reduce possible unravelling. Pin only between where the two rows of stitching will be, and seal the pinholes and seam after completion.
Sometimes the above seam is not possible, in which case consider the classic seam we see on all the cheaper tents: Sew the edges together, and cover the joined edges with binding that is wrapped and sewn over the stitched edges. Look in the shops for binding that has a woven, rather than a raw, cut edge as found on the binding on the cheap tents that is made of strips cut out of the tent fabric. Even this type of seam will hold up fairly well if the edges of the fabric have been hemmed and bonded first, before they are joined, but it does not look as good as a the first seam described above.
Hope this is helpful.