I shouldn't do so as others have already rained on your plans but some things need to be said even stronger than have been.
No, you cannot just use your local sand. It is dirty no matter how pretty it looks. Dirty sand makes for weak (or no) concrete.
Standard mix is 1 part cement, 2 parts sand, 3 parts agregate (or is it the other way around. Been a long time since I mixed from scratch.
You will almost certainly need a permit. They will not issue one without a plan showing what the footing is, width/height of wall, placement of re-bar, etc. You haven't shown that you have any concept of retainer wall design, that is so basic to the project that without that the wall will fail just from the weight of the sand behind it.
Even if you were to take time off work you will not hand-mix that amount of concrete in any reasonable amouint of time even using a mixer.
You say a truck can't get back there. Well, every pound of cement, gravel, sand will have to gotten back there somehow. Pre-mix can pump the mud back there with no problem. You could build the forms yourself or have them built (a whold field of knowledge in itself) and buy pre-mix - probably find that the cost of the concrete in place would exceed by much your cost of mixing it yourself.
Don't worry about the delivery cost of purchased blocks. It will probably run in the 2-3 dollar/mile range (last time I had it done it was on $1 per mile), very minor add on to the a truckload order.
Harry K