Just some of my thoughts:
I really am not a fan of Ertz at all. I think he'll struggle with blocking in the NFL and he isn't a good enough route runner to make up for a lack of real speed vs an nfl secondary. With this draft, I wouldn't be surprised to see Ertz fall to the late 3rd. I know that not a lot of people agree with me on this, but I really am not a fan of his.
I don't see Harrison making it to the 5th. I would be extremely happy if we took Harrison in the 3rd. If I'm honest, I think Miami will take him in the 2nd or the 3rd.
I personally really like Menelik Watson, I think the competition between him and giac would be pretty good. Which fits the mold that JS and PC look for in their draft picks (can compete for starting jobs immediately. Surce: JS interview @ 2012 combine).
I really don't think we go DE/DT at all in the draft at this point.
While I like Ertz a lot more than you do, I agree that the 3rd round is a possibility for him. His stock is on a tumble.
Harrison has the tools to be a 3rd round pick, but not the track record of production. Players with similar tools have gone undrafted in previous drafts (Danario Alexander, etc). This is a loaded WR class and while Harrison could go much earlier than the 5th, I don't think he will. Too many WRs will be drafted ahead of him. I think he'll go 5 to UDFA range in this ultra competitive WR draft class.
If Seattle had taken Watson at #25 I wouldn't have complained. Combine numbers were a big let down, but he has "wow" athleticism on tape. Really good mauler in the run game too. It is a touch optimistic to get him in the 3rd, but after his combine it could happen. The 2nd and 3rd rounds will be completely unpredictable this year, and you'll have plenty of fringe 1st rounders hanging around in the late 3rd.
DE, probably not. DT, probably will. We basically swapped Jones for Bennett, but Branch and McDonald are both FAs and may not be back. That means we still need to add 0-2 DTs just to cover our basic roster. Bennett is more of a 5-tech than a 3-tech too, so adding another 3-tech and some Red/Mebane insurance is still pretty important. Remember too that Jaye Howard is taking a roster spot right now, and he is a decent bet to not make the 53 man. So you might need as many as three more DTs.