Joe,
We exchanged emails about two years ago while I was building my garage and you were in the planning stages. Glad to see your project is finally being started.
I agree with several of the above comments that you are really asking for trouble if you don't have a detailed written specification on every aspect of the project, including work done by the subs. I also agree with those who feel getting too detailed with a busy contractor may chase him away. However, you seem to have found a cooperative builder you can work with. Without written details as part of the contract, you both will have different ideas on what materials and workmanship will be used and this is normal. But, this will produce conflicts during the build and the end result will not be pretty.
I suggest you sit down with your contractor and get him to talk about every aspect of the job, what specific materials he will use, exactly what he is including or not including in the build and to review his terms which are not good for you as written. If this conversation is held in a cordial and cooperative manner, you will get a full understanding of exactly what you are getting. Then, together, you can write up specs covering the details that are now almost totally lacking in the contract you posted.
Too many owners rely on the architectural plans, falsely thinking they should cover everything. But, there is simply not enough space on plans to provide enough details and that is why separate specifications need to be part of the contract. For my garage build, I prepared a seven page spec that covered everything I could think of and made that a part of the bid package. Yes, it scared some bidders away but you don't want those guys anyway if they refuse to bid because they won't be able to build their way or won't be able to slip things by you. My original bid spec had a lot of cooperative words indicating I would be open to spec changes if the contractor could suggest better ways of handling any aspect of the job or could substitute materials without compromising the quality of the job. In effect, you are telling the builder exactly what you want but are open to any suggestions he might have for improvements or cost savings. After selecting my contractor, we sat down to review the specs and made a number of changes in both the plans and specs. After all, an experienced contractor knows more about building than any owner or architect and he should be listened to.
If you want, I can send you my specifications to give you an idea just what you should be getting in writing from the contractor before you sign any documents. It's not a matter of whether you trust the builder, it's a matter of you both understanding what each of you expect in the details of the build. PM me.
Glen