Why on earth do you bill by the hour? You should be doing fixed fee based on value.
The milestones become another form of hourly/daily/weekly plus you have the added responsibility of meeting goals or you do not get paid. Hourly provides pay for time spent.
2/ Currently, I work at a contracting company. Their work is erratic. Between bug fixes and new features with constantly changing roadmaps, I think it would be hard to translate shifting requirements to fixed fee.