Well done
1- I would get it looking like a childrens bed room don't go overboard just tidy clean will be fine but do mention straight away that if you go ahead that will be the spare room subject to you going to panel, shouldn't be an issue as from what you have said older one is hardly their.
2- I usually give the house a once over before any meetings I have, but don't panic to much a a good clean will do
3- fostering is one of those things I am afraid you wont know if it siuts until you have taken the plunge it took us till our second child to really get into the swing of things
Sw can't really give you an insight to fostering as they don't foster,
But you will be asked why you want to foster
To be honest I think you want to do it but are scared and I for one think people who are to sure of themselves are a little worrying so just relax
4-I would ask what age group they think you should do
Do you want to do respite,longterm , short term, or mother and baby fostering or siblings.
Ask what support their is for foster carers
Also I would take a sneaky peek at their ofsted report
How many foster carers they have and what sort it will help you work out what gaps their are for instance if they already have lots of baby carers they may be not very keen if you want to foster babys Ect
Good luck