Having led similar projects myself in the past, I will stress that you first-and-foremost need to construct a "technical project plan." Gantt-charts and the whole shebang.
First, inventory every asset in your project and make very sure that you have source-code representations of them, especially those old AS2 assets. You probably should plan to convert all of those to AS3.
Then, get a handle on all of those external libraries – what are they, what versions are they, what do they actually do for you, and do you have source-code for them.
The bulk of the project plan is in the research leading up to it – determining, step by step and asset by asset, exactly what this project will have to be when re-mapped to a Haxe context. The two environments are not the same and, even though “helper tools” exist, they are of limited usefulness. You will not be “simply porting” this system, but in some ways re-engineering it.
If you take a month – or more – just to develop this detailed project plan … which you might wish to post here (in part) for “peer review” … it will not be time nor money ill-spent. Quite the opposite: “don’t spend one thin dime ‘writing code,’ except for investigative or proof-of-concept purposes, until you have it, and have just cause to believe it.”