I apologize in advance for this super long post
I wouldn't mix the two cuts in an eternity band personally. Rose cuts *seem* twinkly/shimmery to me, not blingy (I haven't seen any in person though, just videos and pics). It'd be a lovely look, just different. It all depends on what you want.
I'd only get rose cuts if you want them, not settle for them because they are cheaper. If that were the case, you'd probably want a redo down the line. I've learned it can be cheaper to do it right the first time than to start over again. It may cost more but would be cheaper than doing it twice
. That said, Kelpie's rose cut band is beautiful, love the engraving!
If you want bling I'd save up for the moissy OECs or diamond OECs (maybe buying one or two stones a month until you have enough for the band).
In the past month I've bought two 4mm OEC diamonds for the same price as the 4mm moissy OECs (with stones that are 5mm+ moissy OECs are more budget friendly than old cut diamonds). I know of a few vendors on ebay that accept offers even if they don't list it as an option. If you are really particular about faceting matching, moissy OECs may be the safer bet. Old diamond hunting can sometimes take a while as you have to wait for the right thing to pop up. It is fun though!
If I were you, I'd buy a few rose cut moissy and see what you think. If they speak to you, order more and get a band made. If not, start hording OECs until you have enough.
Who is the source of the rose cut moissy? I'd love to get a couple to play with!