Downloading forms, reports, minor customizations for Dynamics AX?

I guess what you mean, is you selling addons yourself without going through the Microsoft Cetification process.

Well definitely you will sell some, but how many, and how much money you will make is another question. In the Navision world, the companies that have made money doing this, did so by looking back at their last hundred or so Navision implementations, and asking them selves "well what little bits of functionality do we keep doing" and then after many years of experience with that functionality, and finally gettting it right, they create it as an add on and sell it. I can not give statistics, but from my experience, between one in five and one in ten get this going to the point of it being viable. BUT all the successful ones I know of, are now selling their add ons as certified though Microsoft.
Also keep in mind there is a huge differnece in selling add-ons and selling verticals. When you sell an Add-On, the client is expecting to see a huge databse of installed product, and years of practical Axapta experienc and problem solving. With verticals the client is more interested to see you industry experience, or as they sayl; the ability to "talk the talk".


It is not easy, and definitely not fas, but anyway your questions:
1/ Yes but you need a product. They are not going to pay for "Hmm I could develop this add on for you" you need to provide references.
2/ A good place to start is to look at the MBS pricing model, and look at what granules sold for.  I don't knwo the pricing for Axapta, but compare like for like, and of course the client knows they need to pay a little more, since you will sell a lot less. But only you will know the value of the product, since its you that has the experience of sellign this to cusotmers.
3/ If you can't answer this, you really can't get started. Again as I mentione above look back over the last few years, and see what customizations you did the most.

I would like to add, that even if it would work for you, I would still advise you to consider doing it for free.

There are plenty of resources on the web, that provide very good add-on and all-in-the-box solutions for Dynamics AX.

And they are distributed freely (GNU licence)

Please, reconsider. I think it would be unfair to the rest of the world working with DAX.

 If not, well, then just, anyway, good luck on your development.