I've got the feeling that you either inherited this home or bought it thinking you would have an easy go at removing paint from brick. In any event, you're talking your way into a lot of work. BUT, if you're patient, your efforts may be well rewarded.
I know there are environmentally friendly cleaners out there to help you. For starters, I suggest you go to Alta Vista WEB Search Engine and enter in the following search string: +"removing paint from brick" Include the '+' and " characters. Then press the Search button. You'll get a few 'hits' that talk about removing paint from brick, some of which talk about biodegradeable cleaners. In some of the 'hits' you won't actually find a hit for the search string. When this happens, look for things like Discussion Group links, Forum links, Products/Services links, etc., etc. which is where this topic is 'discussed'. I found a product called Bronz Glow that talks about safe cleaners. Click on Products/Services, then click on Products, then click on Cleaners. Good luck on this!
In my view, painting brick is a mortal sin. As far as sealing up the brick when you're done, if you end up removing the fired layer of the brick (the outside layer), then the 'inners/guts' of the brick become exposed and I think a sealer would be harmful. Why? Because brick is suppose to breathe. If you seal it, you've prevented just that. At the same time, by leaving the inners of the brick exposed, you speed up the process of weathering by an enormous amount. In short, whichever method you use, I'd use the one that leaves the fired layer of brick in-tack as much as possible! And if you have to use dental tools to do the job, that's what I'd do (and people have). If you end up determining that leaving the brick is the best non-thing to do, you probably did yourself a favor. At worst, you can move (and I mean at worst). PS: When we were looking to buy our first home, we found one that was perfect in every way except its brick was painted white! It ruined the whole thing. So, we continued looking and found the real home of our 'dreams'. :-) Why people paint brick is beyond me.