Why do you “have to” do this? Is it just a very strong urge? I think most type designers would say that the notable omission from Opentype is support for multiple masters and non-linear scaling of features. But this has been discussed before (search), and the omission may be justifiable on the grounds that such features should be in type editors rather than in fonts.

Maria, if you do a search on “opentype” you’ll find more info than you probably need. To start with, i might suggest the wiki article on opentype, which will shoot you off to several different sources of information.