I would think hard about so much annual rye. If you mow, it won't have a chance to go to seed, thereby, in a couple years, 25% of your planted seed will have been for naught.
Also, pay attention to both seed rates and cost. My 2 local suppliers typically have different seed preps. 1 likes to provide seed with coating. Now, this coating helps that individual seed germinate and grow, but the coating also makes up approximately 40% of the weight/bulk of the seed. So, in essence you will have a higher germination rate of fewer seeds. Most folk around here buy bare seed, plant it a little heavy, but insure they plant it well. (Right depth, etc)
Finally, I would NOT recommend mixing it yourself, regardless of the cost savings. You will never do as good of a job as someone with a large mixer.
These are just my thoughts. I am in the process of putting in horse pasture, and have gone over this in ridiculous detail. I have been in contact with U Kentucky Ag/Botany dept as well as my local County Extension agent.
The Extension agent was the person who talked with me about how horse handle mixes in the pasture. ie planting Timothy in the mix will only last for a few years, because horses prefer it, and will selectively eat it thereby causing other less palatable grasses to mature past any palatability and also to stunt and ultimately potentially kill your Timothy. He said, probably the best mix (and what I am going with) is Bluegrass and Orchard grass. I have mares, so cannot/won't have Fescue, even though the new strains don't have the endophyte. I won't be able to determine a rogue strain vs planted, and I don't want to lose foals.
This is just a few thoughts which are guiding me.
I am planting TEFF this spring/summer for ground cover and forage. It will provide hay and keep the weeds beat down. It is also cold sensitive, so will die out on its own this fall/winter. I currently have 11 ac in Blue/orchard planted last fall. I will plant the remaining 70ac in permanent Blue/orchard this fall. I'll sacrifice the 11ac for grazing this fall/winter and rotate horses as needed next summer.