Nice budget. As far as receivers are concerned, your 876 has a very good amp section and is enough for 99% of the world. Therefore, if you ever do wanna add amplification (if you even need it to begin with), I am led to believe that a 3ch amp, or even just a 2ch amp would be enough.
Bipoles, you will get a different opinion every time. I opted for bipoles, hoping for better coverage over two rows, after reading an AH article, but I was hoping for more (it seems subtle to me).
So, only in my own opinion, I don't think it's worth splurging on bipoles, depending on the price differential. (Mine cost double the matching bookshelf.) And especially if you don't have multiple rows. However, some others even with one row still really do prefer bipoles. Yet, I think significant improvements to the LCR will not be subtle at all, and therefore blow your money there first is what I say.