I work with multi-track and use DP 5. My projects generally range from 15-30 tracks, although I did one project with 40 tracks (multiple guests). It did take a while to understand it, which was primarily due to learning terminology and where to find various functions. The user manual is difficult to use, but the MOTU board can be quite helpful. I began using DP because of the price break when it came bundled with the FW interface. At one point I tried using Mackie Tracktion, but gave up when I realized 1) I had become fairly fluent with DP and didn't want to learn a new program, and 2) I thought Tracktion was using significantly more processor than DP. Whatever complaints I have are minimal compared to the headache of learning something else and the cost of Pro-Tools.
As for a control surface, I use the Mackie Control Universal. I considered several, but in the end decided to pick up the MIDI based Mackie used (out of production). My decision was primarily based upon the fact that I had MIDI I/O available on my FW interfaces, but don''t use MIDI for anything, so the bandwidth was sitting there doing nothing. Since much of my work is done on the MacBook Pro I didn't want to dedicate a USB or FW port to a control surface. I have been happy with the MCU and use it for all my mixing and automation, scrubbing, time shifting, etc. I don't use it to control my plug-ins, however, but would if I had the C4. I wish I had an extender for an additional 8 channels of faders, and at some point I will. For now I've gotten pretty good at arranging my tracks to be adjacent to each other for mixing and automation.