I agree they will sign a WR. But I don't think Moncrief will be here regardless of what they do.
I also want to sign established FA OL. But this past offseason was the time to do that. There were several options available...but Ballard did nothing. They will probably still sign someone next year...but the group won't be nearly as strong. And this probably means the Colts will end up paying Mewhort $7-8M/year...ugh. Most likely Ballard will look to address the OL in draft.
Unfortunately, DL is probably the strongest position in FA next season. And with the group the Colts already have (including guys on rookie deals), I don't think Ballard will look to spend more on it.
Fortunately, the ILB group has some depth in FA. I have no idea why Ballard didn't make more of an effort to sign Brown, but he will be available again...as will a few other players. The Colts desperately need to upgrade the ILB group. Likely, they will need to draft one to get a great one, but they need to do something. Bostic and Morrison aren't NFL starters...especially when the Colts (and most teams) run nickel defense 60% of the team.
They also need a RB to pair with Mack. Fortunately, next year's draft is deep at the position, as it was this past season.
I think you will see a focus on the offense in the offseason/draft...mainly OL, WR and RB. And on defense, the focus will be on getting LBs and a CB. Between FA and the draft, I think they can bring 7-8 new players that can fight for starting spots across the offense and defense.