Yup. Definitely. Always prune straight after fruiting. Cut out any weak or dodgy branches, branches that are crossing another one, and branches that are growing inwards towards the centre of the tree. Trim for height, too.
Give them time, mits, they will ripen. Ripening is down to temperature rather than direct sunlight. Optimum temps for ripening are anything above low-20sC. The ones in the photos have already started to change colour so they're on the way.
The female flowers (that produce the cukes) aren't being properly pollinated, Jean. If they're indoors, the insects can't get to the flowers to transfer the pollen from male flowers to female flowers. You might need to pollinate by hand.
15cm sounds like a reasonable size. If they've turned dark green and are nice and firm, harvest one and try it as a guide. Leave them too long before harvest and the seeds get too big and the cuke is coarse.
My butternuts did something very unusual this year. Produced female flowers first. Never seen it before. Probably never see it again.
Andrew, it's worth looking at why the extensive foliage. Are you feeding the plants? If you are, and with a nitrogen-rich fertiliser, you'd be encouraging leaf growth at the expense of fruit.
It doesn't look fungal, Mike. Even if it were, with only 6 weeks left, it's not worth worrying about. With 6 weeks left, any toms that are going to ripen for you will be far enough advanced not to be compromised.
Daisy, curling leaves are very very common on toms. Usually nothing to worry about. What are your temps like? And how often are you watering?
nickharr, male flowers always appear before the females. You just have to be patient. And, given that they're in a polytunnel, it's likely you mightn't get the amount of insect life you'll need for pollination. You could need to hand pollinate to guarantee fruit.
Yes, try again, Mike. If the spots have a "bullseye" centre to them, it's likely to be a fungal problem. But we'll have to wait to see the photo.