Will you be living in England or Wales? If so, the following applies, but if you'll be moving to Scotland, they have a different education system.
At what age/school year does formal education begin? Reception or Year One?
In England and Wales Reception is the start of formal education (before that, you have 'Early Years' or Nursery which is for children age 3-4) - if attending a state (not private) school, it is compulsory for children to start attending Reception in the year or term before they turn 5, depending on the policies of the local education authority.
So, say if their 5th birthday is between 1 Sept 2013 and 31st August 2014, they must start Reception in either September 2013 or possibly January 2014 (depending on the local council policies).
Are Reception classes usually physically in the same school as Year One classes? (ie. Is it the same group of kids that go from Reception to Year One? Or will there be all new kids at Year One?)
Yes, primary schools generally house 7 years of classes: Reception to Year 6, although they may be split within the school into Infants and Juniors or First and Middle school.
The different schools are:
Nursery/Early Years: age 3-4 (Nursery class)
Primary: age 4-11 (Reception class to Year 6)
Secondary: age 11-16 (Year 7 to Year 11) (Year 11 GCSE exams are equivalent to a US high school diploma)
Further Education/Sixth Form: age 16-19 (Years 12 and 13 for Sixth Forms) (equivalent to AP classes or freshman/sophomore college classes)
Reception isn't really a separate entity, it's part of primary school - when I started primary school (1987), it wasn't called Reception class at all... the school classes were called Infants 1, 2 and 3 (now Reception, Year 1 and Year 2) and Juniors 1, 2, 3 and 4 (now Years 3, 4, 5 and 6).
When do you apply for school?
I'm not too sure, actually - I know of some parents who register their children for chosen schools (or put them on the waiting list) 2 or 3 years before they will be attending! I think it will depend on the local area and how in demand the schools are... you would need to contact the local authority of the UK town you will be living in to find out.
Do you have to be living in the UK to apply?
You need to know what council district you will be living in in the UK, so ideally you need a UK address... because the schools have catchment areas which determine which schools you're likely to get preference for.
I guess I'm trying to figure out would it be best for our son to start school in the UK at Reception or Year One? Is it more advantageous for him to do Reception in the UK?
If you move to the UK before or during the year that he turns 5 years old, then he must start Reception... you have no choice in that, unless you choose to home-school or send him to private school.
From what I've read it sounds like you have to apply a year in advance and that you have to be in the UK. Can you apply from overseas? How does that work? Do you have the same chances applying from overseas as you would applying from the UK for your preferred school? or would it be better to apply from within the UK?
The problem with applying overseas is that you need to apply to the local UK council for the schools... and if you are living abroad, then chances are you won't know where you will be living in the UK yet... so you won't have a UK address to use for applying.