I read your pm but though it might be useful to post my thoughts publicly.
I have a DS at WHSB (yr12) and a DD at WHSG (yr7). We live about 6 miles north of Braintree. When DS was offered a place at WHSB, many people though we were mad to take it. Indie was not an option.
I work about 1 mile away from the schools so on most mornings I drive them to School. Both get the SBC bus back to White Courts where my wife picks them up.
It's a long journey but they both very quickly got used to the idea and it has become just another part of the school day. We, as parents, worry about this stuff far more then the DCs do. Obviously the long journey eats into evening homework time and can restrict their socialising but this is fine with a bit of careful time management. However, many children attend both Westcliff schools from great distances so they are not alone.
Both schools are conscious that some DCs have to travel a long way, but occasionally School trips arrive back after the bus has departed when you will have to make alternative arrangements. You will be given plenty of notice in the circumstances.
As for SBC, they are very good indeed. They took over the contract from a smaller firm in Chelmsford with whom we had regular problems but in the 3 years SBC has run the (now 2) routes, it has run very smoothly. Good quality coaches all with seat belts and no issues on the coaches themselves. Kim and the people who run SBC are great. http://www.sbcleisure.com/
I have no affiliation.
The route from WC has only been operating for just over 1 year but is popular and will only grow I suspect
You should certainly look at WHSB. It's a fantastic school. The HeadMaster is rather "old school", strong on discipline, does not suffer fools at all well and runs a tight ship. It's fair to say you'll either love him or hate him. Personally, I'm a huge fan. Very well run school which now has/will have academy status. Outstanding ofsted etc - you can find this stuff pretty easily so I won't go on.
Don't get suckered into being told that the Westcliff Schools are the poor cousins to Chelmsford and Colchester. They are not. They have a slightly different selection criteria which favours local DCs to a point, but you apply in exactly the same way as any other school in Essex. Read all the CSSE stuff and it will be no problem. It will interesting to learn if this will change with its Academy Status - another discussion.
Hope this is helpful to you and any other parent in a similar position but please shout is you have any other questions. DD is no 3 at a Grammar school (we have another DS at KEGS) so I'm a bit of an "old hand". No 4 is only in yr2 so I've got a few years off!