I've been in your position twice, which has made me learn quite a bit about line (but certainly not as much as a pro).
Double check your lengths. The mast on my 28' boat is 37' tall and I need at least 95' of line to bring halyards back to the cockpit. The length required needs to go from the cockpit to the top of the mast and back down to the base of the forestay.
I prefer larger jib sheets to the main sheet. The jib sheets have no mechanical advantage when you aren't using a winch, the main sheet should have at least a 4:1 block setup. The limiting size on the main sheet is what will fit through your blocks, where jib sheets are only limited by what works with your winches. The downside of going too large on jib sheets is that they'll be heavy and will weigh down the sail in high winds. These days sizes are based more what on what is comfortable to handle, not required strength.
I spend the money for low stretch lines (like Samson XLS Extra) on halyards, but not on sheets. 3% stretch (typical of double braid dacron like XLS or Sta-Set) on a 95' halyard is a lot and will prevent you from getting a high luff tension. 3% stretch on a jib sheet seems like less of a big deal since the sail will also stretch under high wind loads. Dyneema-based XLS Extra has under 1% stretch, double braids like XLS/Sta-Set/Novabraid are about 3% stretch, all measured at 20% of breaking strength.
On my 28' boat here is what I'm using:
* Main/Genoa halyards: 95' XLS Extra T, 3/8"
* Spin halyard: 95' XLS, 3/8"
* Main sheet: 45' XLS Extra, 7/16" (mostly because I got an offcut for a good price)
* Jib sheets: I didn't purchase them, looks like 35' each of 7/16" Sta-Set
* Vang: 3/8" XLS
* Reefing: I plan on splicing 3/16" Amsteel (bare dyneema) to run through the sail, then bring that down to 3/8" XLS for running through the clutch and winch. Amsteel is really slippery and low stretch, but doesn't work well with winches or clutches.
* Outhaul: 3/16" Amsteel with an eye splice on either end. The end by the mast is connected to a 4:1 tackle and that connects back to the clutch and winch with something that looks like 5/16" XLS.
* Topping lift: 1/8" Amsteel from the masthead to the boom, holding a block. 1/4" Novabraid (cheap XLS substitute) tied to the boom, up to the block, and back along the boom. 1/4" is fine here since this isn't adjusted under high load.
* Lifelines: 1/4" Amsteel on top, 3/16" on the bottom
When I replace the jib sheets I'm tempted to go with 3/8" Salsa Braid, which is really light and feels nice in the hand:
New England Ropes Salsa Line - Dyneema Blended Single Braid - Competition Grade Rope - Cordage - Downwind Marine
It's expensive though compared to double braid dacron.
Watch your local stores for offcuts. It's hard to find them in long lengths for halyards, but pretty easy for shorter lengths used for sheets.