About (2) I think programmers don't buy development tools any more. They use open source or maybe free tools. Only Microsoft might still be able to have people pay for Visual Studio (but that's because they own Windows).
Either your project should be open source or it should be aimed at non-programmers like finance or accounting people.
I think the best plan might be to create an open source tool first and then, when the product start to be good enough, sell special packages around it for finance/accounting.
I think you are using a massive brush to paint all "programmers" here. There are many types of programmers working on many types of software. Many if us buy dev tools. There are not open source equivalents for everything
I think even more important question is "what essential dev tools you've purchased that had some sort of open source equivalent".
As for me, last thing I remember – I've purchased http://theolabrothers.com/sip/ when is wasn't free. And it is just a simple tool I don't require at all (any image editor can be used instead), it is just much more convenient than any other alternative.
My current plan is to make runtime platform open-source, but sell hosted development tools as SaaS.
While software developers don't usually buy platform stuff like compilers, libraries etc – they are usually more than willing to buy products that make things simple. Otherwise companies like GitHub or (my own product – Hosted CI) won't get any revenue.
Either your project should be open source or it should be aimed at non-programmers like finance or accounting people.
I think the best plan might be to create an open source tool first and then, when the product start to be good enough, sell special packages around it for finance/accounting.