Make a Battle Plan seems fun. I wonder how it plays out! I assume everyone in the unit will Help, and so the 3 holds will be the norm.
From the couple playtests I’ve run, usually the officer or the sniper make the move, since they have high tactics.
Helping is not as common as it might seem. First and foremost, you have to have some way to help (not saying that’s an issue here). Second, helping or interfering is not a guaranteed success. Like AW, there’s a chance that you expose yourself to “danger” and there’s always a chance you’ll miss and make things worse. It’s that chance to screw things up, I think, that acts as a deterrent. I think that is particularly true when you do have an officer or a sniper make the move, where they have a pretty good shot at succeeding to begin with.
From the wording, it sounds to me like the roller gets to invent what the opportunities are. In this case, when I rolled to Help, I think I'd be lobbying for an opportunity that suits my character's strengths (or my idea of what's fun), so I'd be getting that +1.
The person making the “Make a Battle Plan” move makes the call as to what the opportunities are. That said, the way a character helps is by bringing some new insight or important information to light. So, as the helping player, you could slant that information or insight toward your interests if you choose to. If the information or insight you bring to the table is juicy, good odds that the player making the battle plan will jump on it.
It also sounds like the roller gets to invent the map. Is this correct? If not, you might want to repeat the "ask the GM" language that appears in the Assess move.
The big picture map, in theory, should already be there. It’s the GM’s job to paint a picture of the world and one of the ways we suggest doing that is by drawing maps. Of course, the part where we say that hasn’t been released yet, shame on us ;). So, good question.
What this move is getting at is that you either sketch out your own map or overlay one that already exists on the table with your plan. The move allows you to add new details – opportunities – to the world that the GM’s already described* for you while at the same time, describing to the GM and the other players how you intend to carry out the plan.
Example from one of my play tests: GM has an area map on the table and the players just got their orders. The officer orders the sniper team to set up an overwatch position above the objective. The sniper makes a battle plan and hits on a 10+, getting 3 hold. Looking at the GM’s map, the sniper sees that there is a fair amount of ground to cover and a ridge near the objective, so the sniper spends the hold to 1) establish that there’s a ravine they can use to conceal their infiltration 2) there’s a good snipers nest on the ridge that overlooks the objective and 3) the sniper knows the range to the objective (for the doped scope move). The sniper follows through by making the infiltration engagement move and gets to the vantage point undetected.
*As in AW, the players are always empowered to ask the GM for clarification or extra detail about the world around them. So your suggestion about adding the “Assess” move already applies in general. The “Assess” move itself is intended to allow players to gain new or special insight into the world, rather than simply a better understanding of the world their characters are already enmeshed in. That said, “Assessing the Situation” is a great prelude to “Making a Battle Plan,” so if you’re looking for that edge, assess, then plan.