We do both, single and two man, depends on the work, tbh I would get your current set up to a 2 man system because it's going to be a good three months before any employee will be up to speed/technique and attitude you want to instill in them, that's even before they are learnt the rounds and you know they are trustworthy.
The two man set up allows you full control over an employee, once fully trained, know the rounds and your happy they will be reliable you can then move forward and get a van suitable for a single operator ( Citroen dispatch or ford connect are ideal )
On average our 2 men teams achieve around 60% more than a single man ( say £300 for a single a two man will do around £450 to £500 )
But it's dependant on the round and how compact it is and the number of cleans that can be done in a stop without moving.
For conservatory, SFG cleans, larger works/commercial 2 men can usually produce twice a single, as they get less tired with the more demanding cleans
HTH
Darran