This mod is very nice feature-wise, but the GUI needs a lot of love.
Some suggestions:

• Grids should look like chests
  • which includes the font rendering
• Grids should have scrollbars
• Grids should have a toggle to auto-focus the search bar
• Grids should have a scaling option (e.g. 3/6/9/12 rows)
• Everything should be centered/aligned
  • buttons and such
• Every GUI should have a title (e.g. name of the block in the top-left)
• Priority inputs should be input boxes, not a counter with +/- buttons
  • sidenote: given the name "simple storage network", having inverted priorities is confusing, higher number should be higher priority
• Storage Request Table should have a tooltip on the crafting output
  • there is no indicator what left/right clicking does without trying, wasting resources

For just general design I'd look at how AE/RS/Tom's does it, they've pretty much just re-used the layout/design of the vanilla chest and added buttons/scrollbars to the sides, giving it a uniform look.

Aside from the font rendering, this should be reasonably simple job to implement, as it's just some reordering/offset adjustments and some minor texture work.

I agree, the GUI design is ancient, and i havent changed it once since taking over the mod from the other author 5+ years ago. and thanks for writing it down with all the detail. Once i get some bugs cleaned up ill keep this near the top of my list

still planning to look at this .
Also related: gui improvements #357

Priority ref #396

if the toggling of search autofocus is added to GUI make sure to delete the config for it " ENABLEAUTOSEARCHFOCUS = COMMON_BUILDER.comment("\r\n Set to false to disable the automatic focus of the searchbar - client gui screen")
.define("enableAutoSearchFocus", true);"