I'm not quite sure how to respond to this. Have you ever raced before at all? I can't tell from reading the question, yet you're racing a J boat which is popular for racing which would seem to indicate that you have raced.
If you have, then you know (or should know) most of the tips and tricks that I could offer.
If you haven't raced, then I could say a few things...
Sail shape for specific conditions is critical to speed. Similar to gears on a car, a flat shape is fast, and has less drag, but offers less power in choppy water.
Conversely, full bellied sails will power you through a chop, but limit your top speed because the air tends to drag over them more slowly.
Don't be afraid to reef, not just for safety but because a reefed main will be faster than dragging your rudder through the water like a brake or sailing with the main way out, spilling wind.
After tacking, don't have your main trimmer haul the traveler fully to centerline immediately, get some way on, and then bring it up as you build speed. You (helm) and the main trimmer need to be in sync so that the main's trim isn't overpowering the rudder.
Mark your helm (wheel) with the rudder centerline, and then the maximum amount of allowable weather helm on either side of that. If you find yourself steering past one of the "maximum weather helm" marks, your main is overpowering you and you're dragging the rudder. Trim accordingly.
Please understand that this is all very generic because I haven't ridden and J boats yet, and don't know their particular characteristics. Hopefully some J people will speak up.
As far as night sailing goes, have a backup GPS, designate a navigator who knows what the heck they're doing, have a functional depth finder and a radar would be nice, especially on a 40' er. You can use it to see rain or squall lines. If you're lucky, there'll be a moon by which to steer and observe the clouds and wind speed. If you're unlucky, you'll be navigating in an inky blackness, by instruments only. Post a lookout with binoculars.
Rigging: I find that large knots on the genoa really slow down tacking. Yet, if you "luggage tag" the genoa, it makes changing a head sail a real hassle unless you use multiple sets of jib sheets. You can splice eyes into the ends of your sheets, and then use a small piece of spectra/dyneema to make a "soft shackle" to join them, and it'll slide smoothly over your shrouds, improving your tacks.
S/V Old Shoes
1973 Pearson 30 #255