You mention liablity and contracts. You should ask a lawyer what you need before doing anything. Then ask a CPA, really important if there is a chance to do any thing beyond a little beer money. Don't know your plans but the first into the second year we were in business we ended up doing a lot of business unexpectly. Didn't get to see any of the money because we hired people, bought business stuff, opened a couple offices without knowing where our next paycheck would come from but hoping they would continue to come in. You don't want the IRS on you though especially in this kinda situation where the money is spent but possibly isn't accounted for well because you've never owned a business and don't know what exactly to do.
Anyway, at minimal my suggestion, and I'm not a lawyer so you should confirm this through your lawyer, would be to form an LLC which gives you some corporate protection. Do your contracts and operate through the LLC. If you run over a home owners dog (or worse) the LLC is liable, not you. I know it sounds shady but if you are doing "Company Work" you need to do it through the right entity. If the customer doesn't require you to have insurance then they should reasonably know if there is a problem they might have a hard time collecting. If you do enough business to afford insurance get it and get it to cover your equipment as well.
Think of what could go wrong and have the Lawyer draft up a quick contract for you to give customers including this stuff but don't make it so harsh they think you are shady. Something like "not responsible for hidden utilities beyond those makred by professional utility locating services" "owner is repsonbile to remove all non vegitative debris from the work area" "contractor will not remove or haul off trash and debris unless otherwise stated in contract" "contractor will not haul off excess dirt unless otherwise stated in contract" "this contract does or does not include final grade consisting of XXXXX". This protects you and the customer since the customer knows what to expect there is no confusion. I've known a couple contractors have their name tarnished because of vague contracts even though they are decent guys.
Outside of that there is negligence which you could be personally responsible for such as not calling the Utility Locating Service before starting and causing an explosion. Or drinking on the job and causing an accident.
Sounds silly but this stuff is really pretty simple and can be done in one day. An LLC is taxed like a person so you have to basically do 2 tax returns or maybe a little more but a cpa or good book keeper can explain this to you.
Anyway to the original question. I'd do a 2 hour minimal and offer a daily rate at a discount to attract customers.
Working for other contractors as a sub contractor can be a bear, they are worse than home owners and you better hope they didn't underbid the job or not entail the work required to finish the job to satisfaction.
