You can certainly make a combo DT and have him be effective. My advice to you would be to retire your current guy, to do a bit of research around here regarding how to make a DT, and to re-create your DT on day 40 or day 41.
As for building him, there are a lot of different ways to do it. IMO you should take strength to at least the 8 cap while multi-training speed, agility, tackling, and vision.