That sounds like a very good approach if it is the right amount of volume for the load carried. I used a similar sized set of front panniers with a tent on top of the rear rack on one tour, but didn't need a frame bag or more space of a dry bag on the rear rack for my gear. If I had needed more volume those two bags would have been a good way to add it. I think my gear not counting food or water was 22 pounds on that trip. The setup worked very well and I found the handling to be very good.

My only issue is that the Tangle bag is fairly expensive for not a whole lot of capacity. With the setup you suggest I don't see it as being all that likely to be necessary. Between the front rollers and the bag on top of the rear rack there is a lot of capacity. A little bag that is for items that are easily at hand may be required, but that could be a tank bag or a little handlebar bag. If you really need a lot of capacity maybe four panniers is the way to go (or better yet start trimming the packing list).

The rear rack has the advantage of being able to be loaded up with extra stuff when needed. If you need to haul food and water for 24 or 48 hours between restock, or just hauly groceries, or maybe even haul a load of firewood the rear rack can come in handy.

Of course a Carradice or other saddle bag including a bikepacking style bag could be an alternate asnwer to the rear rack and dry bag.