I have 3/8 Samson XLS for the mainsheet, and a mid-boom traveler setup. I found this setup
for 4:1 on the Jamestown site for Harken, but like the idea of more affordable Garhauer blocks but not sure which is comparable and the choices are plenty. Thinking I need a fiddle block with ratchet, cam, and becket plus another fiddle block on the boom.
119 sqft is a hefty enuf mainsail to be tiring on the arms, when sailing the boat dinghy-style in stronger winds. A ratcheting lower fiddle is really helpful in that regard. Harken's Hexaratchets are good, but very expensive. BTW, that Harken "4:1 mainsheet" is actually only 3:1 with the cleating fiddle on the traveler. Strange, but true.
Attaching to the boom deserves some thought. You can use a fiddle and one beefy strop/bail/bracket, or you can spread the load among two or even three single blocks. I like a fiddle, because it is narrow. But it can require manual swiveling sometimes, and I do advise spreading the spar load. We added one of these hangers
from Ronstan. Wish the shackle slot were wider. We also use 5/16" double braid for all our sheets. It's a little less comfortable w/out gloves, but it may fit smaller hands better & it most certainly runs smoother thru the blocks. Fuzzy 3/8" has enuf friction, you almost don't need a ratcheting block -- but it can be slow to dump in a puff.
Finally, give some thought to whether your cleat should open upwards or downwards. Best option is a lower fiddle with reversible cleat, so you can try both ways. On our Bucc18, the cleat releases upward: the lower fiddle is up on the CB trunk, and you are nearly always hiking way out, so a flip up will release the sheet and recleating (a rare event) can be done at your hip. On the SJ21, the lower block is on the cockpit sole. Cleating is a simple upward tug, but uncleating may require a prod with your foot. If sitting on the rail in windy conditions, we have to hold the active sheet off to one side so it doesn't accidentally re-cleat. Not sure I'm happy with it. It's down to preference and practise.