Hi Holly
Welcome to cockers online.
Its a great idea of yours to get lots of information and ask all these questions before you take the step into getting a doggy.
With regards to the time you would be out of the house I would sadly say that its perhaps too long...I can only talk from experience, I have two cockers and they are both fine for an hour or 3 but no more really.
I can see what you are saying about getting a dog walker to come in and excercise them for you and possibly if you got them to do this morning and afternoon it would be ok but it can cost quite abit so just look into that first.
With the excercise thingy, I find both mine are fine with one walk a day but I do tend to take them out twice just so I know I have done my best to wear them out
They are a very active breed and do need lots of excercise....just got back from walking mine and was hoping for a quiet 30 mins but the one is still ready for more
Good luck with it.