OK Great! The Welter brassica mix sounds like a great combo for your brassicas and I am sure they will do well. Now...not knowing anything about your deer density or environment I can only tell you how planting just that mix would work out here on my dirt. My deer will have devoured every last morsel of that mix by probably December at the latest - sometimes even sooner, and all I would have left until next planting season would be bare dirt.
If you look at my "Recipe" on the post at the top of this page you can see that I plant a very similar brassica mix as what you will be planting. The difference is that I don't want to be left with bare dirt in the spring. I want to keep my soil covered, I want a diversity of living roots in my soil for as many days per year as possible, I want to continue feeding my deer - especially following snow melt when forage is pretty lean in the north woods, and I want to have at least somewhat of a cover crop to plant into the following summer. I accomplish all of this by planting what you see in my mix above, and by following that July planting by broadcasting cereal rye into the brassica mix 4-5 weeks later after the brassicas have become well-established.
Plant a few pounds/acre of whatever clovers you prefer at the same time you plant your brassica mix - you can mix it right in with the brassica seed and plant it at the same time - no sense in walking any further than you have to to plant. The brassicas won't even know the clovers are there as they will shoot up after the first rainfall and soon canopy over the tiny clovers, keeping them suppressed until spring. Same thing with the rye. If you broadcast rye into already established brassicas, the rye will have zero negative effects on your brassicas but it will be a tremendous boost for your deer in the spring and it will help build Organic Matter (most of which is built by roots under the surface), provide a carbon boost for your soil, suppress weed growth in your plot, keep your soil covered, provide fawning cover until you plant again....and probably lots of other benefits as well.
Believe me, you are not going to experience any "crowding" out of your brassicas by planting this way. There are many, many benefits to this method and few, if any negatives IMO.