Arjan I concur with Jake and Jeff's suggestions above.

A few things:

Mast rake depends on crew weight. In those conditions if you attach a line to the trap wire, take the wire forward to the bridle attachment point on the hull, mark the line, then take it aft to the rear of the hull you should be about half way down the transom. Further forward if you're two big guys, i.e the upper rudder pintail.

Tension your rig by putting one guy on the trap wire, yanking hard and moving the sidestays. Both stays should be even at the end.

Which boom system are you using? Round or square? On my Infusion the outhaul places the clew of the main about 2" from the stern end of the boom. I basically leave it tight unless in light air. The main sheet connects to a strap that runs through the sail and around the boom. Basically you are putting 10:1 sheet loads directly on the leach of the sail. Like Jake mentioned, sheet in, get both guys on the wire and start trucking.

Let the jib traveler all the way out in heavy air. It's experimental on the crossover for traveling in some.

You probably need more downhaul than you think. Hard to say with a loose mainsheet. Sheet hard, take excess power out with the downhaul then start playing main in the puffs. I let the crew have the main upwind in breeze if they are responsible.