I need to rearrange some of the plumbing under the kitchen worktop so I can
push the appliances back further in the slots, & I have a few random
questions about the input & output.

We have a cold-feed-only washing machine in place & a cold-feed-only
dishwasher on order. There are 2 cold connections & 1 hot one; the
hot one has never leaked yet, but I'm a little nervous. Is there a
secure cap I can put over the unused hot connection? Or should I just
remove it & cap the hot pipe off because cold-and-hot-feed appliances
are very unlikely to appear again?

(The strange thing is that when we moved into the house, there were 2
hot connections & 1 cold one.)

What do I need to do (apart from turning the gas off) to make it safe
to solder a joint on a copper water pipe a few cm away from a gas
pipe? Or should I just use a compression fitting?

The two waste pipes currently meet at a T above the kitchen floor; the
merged pipe goes under the floor then runs under the kitchen and
through the wall, where it opens over a drain. I haven't been under
the kitchen floor in a long time, & I can't remember whether there's a
trap in there.

I plan to change it so two waste pipes both go vertically down through
the floor and meet underneath, then run to & through the outside wall
(using solvent-weld). Do I need separate traps for each pipe? Should
I leave a trapdoor under one of the appliance positions in case I need
to unblock them later?

Thanks,
Adam