Mark, get a 600 IBC for your shed - a 1000 is cheaper if you have the room.
Put a 400L in your Caddy if it's payload is 700 or more.
Use a reel. Not barrels/trolley. (I've done trolley, backpack, trailer and van - van is best, followed as a poor second by trailer.)
Get an SLX30. The adjustment of an slx is better/easier than an extreme (IMO) in narrow gaps on domestic. Take the two biggest sections off and use it as an SLX20 on 90% of your domestic work and add any of the other sections as needed.
Canvassing: (wear smart casual or logo'd polo shirt - carry a folder/clipboard)
"Hi, I'm Mark Stone the window cleaner, I've got some customers your area already and I'm expanding a little to make a full weeks work out of it - do you need a window cleaner?" (Shut up and wait.) They will say:
1. No thanks. ( I do my own, I've got a windie, etc)
2. Had one - unreliable. (This can mean "no" or "convince me")
3. How much? (green light)
HTH - if it works, send me a six pack of Wadworths 6X.