moving etc

Hello everyone,
im new here i was hoping a few of you could give me some tips with the
following problems.
my cats are a male and female both 8 years old,ive been in switzerland for
the last 25 years
moved back to the UK 6 months ago,my cats for the last 6 months were with a
freind in Zürich.
Theyve never been outside,were bred as house cats.
They joined me in the UK 1 week ago,they recovered very well from their
trauma flight etc.
What im looking forward to is letting them out for the first time,theyve
both had their inoclutaionsd etc.
Id like to ask you all
1) How long should i keep them inside beofre i let them out?
2) How do i help or thrain them to use a cat flap?
3) After theyve started going out ,should i get rid of their litter box,or
leave it.?
4) Theyve never had collars etc,should i put one on them,will it disturb
them,are they to old.?
5) Is there anything else i need to know?
Sorry about so many questions,but these little clowns are pretty
precious to me! Just for interest,they were reunited with their old freind a
5 year old Jack russell,who theyve know since a puppy.when i got the air
crate finaly in my living room,it was amazing,the dog shook all over with
excitement,then his tail nearly fell off it wagged so much,i let the cats
out of the crate,then the cabaret started,the purred so loud i thought theyd
got throat infections,they then proceeded to rub themselves so hard against
me and the jack russell,that the jack russell repeatedly lost his
balance,ive never seen such joy expressed by animals,they were besided
themselves with joy at the reunion,that night we all slept together in my
bed,i dont normaly allow that but i was also happy to see my freinds
again,anyone who says cat`s dont remember their owners are psycoticaly
misinformed
( i guess no one here ,argue with that
Anyway any help would be greatly appreciated.
Regards Keith