Re: Finishing up a TBH nad have a few questions..
With many TBH designs, you need ALL bars in place to be able to close it up properly and keep the bees/entrance where they are supposed to be.
The 1.25" bars are for the brood nest, the 1.5" bars are for honey combs. Since your new bees first need to build their brood nest, those bars should be 1.25".
You likely will need to inspect to decide when to switch bar sizes.
-- Victor Hugo -- "Common sense is in spite of, not the result of, education.”