Being that you are a self sufficient person consider doing your own concrete in sections. By that I mean doing the mixing on the job. In our area there are several sources of aggregate. To get a proper mix it should not have noticeable "dirt", but also well graded from fine to course. With our crushed dolomite (limestone) for road gravel, that is a great material. Then you mix with 5 parts of this gravel to one part cement and don't make it any too sloppy, since a lot of water in the mix means weaker concrete. Keep it as stiff as possible.
If you go for regular concrete with the sand and gravel separate, that mix is 1:2:4 or one part cement, two parts sand and 4 parts coarse gravel.
To get the strongest result you then keep the hardened concrete moist for at least 7 days. Plastic on top usually is the way.
My background is a civil engineer specializing in construction materials.