I have to smile at the attorney - if you take his 10% up front plus the 60% first day that is 70% - or $5600 - almost the same as the $6000 the contractor wanted. Ditto to the 30% - that is $2400 - pretty close to the contractor's $2000.
Unfortunately -there are no "standard" terms, though jobs with a lot of finished materials like cabinets, doors, windows, appliances, etc tend to require a higher up-front payment than those using raw materials that can be used on any job.
Explain to the contractor your concern, and see if he will buy off on 75% of materials upon delivery and storage at the home ($4500), rest of materials and half of labor ($2500) upon completion of installation of windows and doors themselves INCLUDING delivery to you of lien releases from suppliers of the materials, then remaining $1000 labor upon completion of entire job including trim, any painting, delivery of contractor's lien release, final cleanup, etc. That puts a little less up front, gives incentive to get them installed quick, and actually gives him more money before job end. Don't know if this is any improvement for you, but you wanted another option. In reality, should not make for much difference as putting in doors and windows for a house should not take more than a week at most unless this is a very small contractor.