Ventilation ventilation ventilation. We have doors and louvres at each end, and on warm days those stand open all day (with mesh to keep the hens out) Ours is 21'x42' (7x14m) - any longer and you may have to use a fan in the hottest of weather. Damping down can help, but just on the soil and any surfaces, not onto plants. I've seen me flapping seed trays to get the air moving, but that's inside my greenhouse, which is inside the tunnel, so a problem to ventilate.
Weeds - you do have to do a lot of weeding, but the soil is very easily workable. Keep the weeds under control through the winter, dig deeply to get to the those thistle roots, then be diligent as your plants grow. We get thistles, couch, buttercup and massive chickweed mostly. It's nearly always too damp outside to hoe, but inside I let the surface dry out so I can hoe - best is probably a very sharp, very small hoe, avoiding plant roots and stems. Hand weeding otherwise. I don't use plastic ground cover in the tunnel, as mice nest under it so the dogs dig it up and create mayhem.
For irrigation, we started with a gravity fed 'leaky pipe' system (we don't have mains), so water was delivered to the roots, but after a few years the holes in the hose blocked so now we water by hand, at ground level. Yes, never water from above - my OH did last year and every one of our lettuce rotted away
I soak the ground very thoroughly when I dig planting holes, so the plants sit on wet ground deep down, then I build a little moat of soil around the root run of larger plants such as tomatoes, so I can give the roots a thorough soak, without the water running off. If you keep the surface of the soil between plants dry, it's easier to keep it weed free. There are other tricks such as burying water bottles next to heavy drinkers, so water is directed to the roots. I haven't had much luck with that. Water in the early morning, or last thing in the evening, rather than in the heat of the day.
Having said all that, I never achieve a totally weed free area, just enough to reduce the competition - life's too short