I’ve done Smash Vienna’s and enjoyed the malt flavor. But I also considered removing it and doing a larger portion of Munich. Or even simplifying it to have it be just Marris Otter, Oats, and Dark Malts. I mostly brew hoppy pale ale’s (one imperial stout in the past) so I don’t have a lot of trial and error experience.
I do agree that the vienna and/or munich will get lost in all the roasty goodness. Meaning, that you won’t be able to taste the difference between the two. So I would either go with vienna OR munich, not both. Have you considered any crystal or caramunich malt to balance the roast a bit?
Unless you have an air tight secondary, I would recommend letting it age in a keg instead of a secondary. The recipe is pretty solid, but I would offer a few suggestions. Since pale ale malt is kilned to nearly the same color as vienna, I would eliminate the vienna and double the munich. Lastly, my beers tend to come out a little ash-like once I go over 15% dark roasted malts. Maybe dial each one back a percent.