Steve,

A-OK?

8-)

You will want your power windows (where the hell are you going to get
them from?) to run off the aux side of the ignition switch.

The central locking is useless if the key has toi be in the ignition for
it to work, so it doesn't come off the aux.

Driving lights should run via relays driven by the existing headlight
wiring. If you fit fuses they should have their own dedicated fuses.

In electricals the easiest way is often not the best way. You've got to
live with your wiring for the life of the car - take the time to do it
right.

See above.

What I would recommend is that you do the following:

Cigarette lighter in a Mini is usually run off a purple wire - live
after a fuse all the time. Modern ADRs actually require that the
cigarette lighter only work with the ignition on, but since your Mini
predates this, you can have it on all the time if you want to.

Radios typically work off the ignition (aux) so they turn off when you
pull the key, but modern ones often also require a permanent live to
maintain the electronic memorys and run the clock. They don't pull much
current so there's really not much reason not to simply use the purple
(fused live always on) and brown (fused live after the ignition switch
aux.) to run the radio.

Electric windows pull quite a lot of current which you probably don't
want going through your ignition switch, since it was only really
designed to cope with wipers, a heater fan and the brake lights. Fit a
relay which is turned on by the live from the aux output of the ignition
switch (Brown). Fit a fuse to the live supply to this relay. Consider
seriously fitting a timer circuit so that this relay remains on for say
2 minutes after you turn off the ignition, so that you can wind up your
windows after you've pulled the key out of the ignition.

Central locking needs to be on all the time and pulls a surprising
amount of current very briefly. Whilst you could probably run it off the
existing fuse (purple), I would be inclined to fit a new fuse box for
all the modifications and dedicate a fuse to the central locking too.

Driving lights and headlights in general should not share a fuse with
anything else. Often, as in the Mini, they have no fuse at all, but I
strongly recommend fitting a fuse to any wiring you add, since the the
chance that you will manage to make a minor mistake which will one day
result in a short circuit is much higher than the chance of BMC/Leyland
making such a mistake. The bottom line is that any aftermarket wiring is
more likely to have a fault.

In my Nissan I have the following:

Central locking, an additional cigarette lighter socket and a VHF two
way radio which share a single fuse direct from the battery.

Multiple driving lights and fog lights, which all have relays and fuses.
My existing headlights also have had relays and fuses added to cope with
high power globes.

A replacement radio which operates from the existing radio wiring with
an adapter to suit the plug which fitted the original radio.

I think the best thing to do is to try and find a uncut wiring loom, and add
to that, i have done this and now have my clubby wired with a five fuse,
fusebox. Much safer that the original 2 x 35 amp fuses. once you have the
new loom added to, it takes an hour or so to put it in. much better when you
are using it for a daily driver. Work can be done and you know that the car
will still run!!!!