You sound a pretty switched on bloke and as some have said the cleaning is the easy bit...
150 in that time frame is optimistic but hey no harm in that....but what you need to do is look a little deeper to find out what you really want and need from your business....perhaps running part-time for a periodas you have said will be the best way forward.
Personally I try to make my years money in circa 200 days of actual work...sounds like a lot of time off right?...holidays vech probs, sickness, snow, sub freezing conditions, not todays, late payers etc, etc etc...and this is without the expenses needed to run the actual business which may prove more than you believe right now.
I did build my round with leaflets alone but from this 0.5% hit rate is about right...and putting out say 20k would be a good start.
Get yourself some maps and note down everything you do...the yes & no's, not in's and with leafleting repeat, repeat and repeat again.
This is a no fail business...as someone here once said....get 1 customer clean it, get another customer clean it...repeat, repeat.......I think many on here will have built their round and honed it over 4+ years then again some have built rounds much quicker.
All in all...round building is like cow farming...milk them until they stop producing then cull them as required...treat them nice but don't give them names and invite them into your house for tea!
Or you could buy a full/part established round?
Cheers and good luck...keep us posted...