Another teacher here. I have investments in both a 457 and a 403.
A question: You mention that your district and others formed a trust and use VALIC for individual plans. Does each district administer its own employees plans, or is there another plan administrator? The reason I ask is that school districts, depending on size, often hire a third party administrator to service employee plans and handle paperwork (of which there is a bunch). If not, then someone at your administrative office is more than likely tasked with this, and so you will have to go to them to find out plan specifics.
Is there an expense difference between your 457 plan and your 403? and what is VALICs take?
If it were me, I would put my money into a 457(b), but only because you might still be able to take withdrawals before 59.5 without a penalty should you need to. This is possibly going to change with the new tax bill, if it is signed into law. But who knows. I would also ask your plan administrator if you are allowed to contribute to both a 403 and 457 concurrently. It is one of the few perks that teachers enjoy, and it looks like the tax bill is going to allow us to keep the ability to contribute to both. But it will depend on how your plan is written. Later on when you increase your savings rate it would mean being able to set aside 36K per year, and would get you to your desired tax bracket pretty quickly.
VINIX and VBTLX are both fine funds. I have used VINIX in the past, and think that a fund that tracks the S&P 500 gives you plenty of exposure to the total market.