Hi

Welcome back

in answer to your questions, I would say

1) JEDI-SDL units - if you are using SDL these units have been modifed to work with SDL. They also support Opengl 2.0 (tested under windows and linux) I think the dlgOpengl units only support Opengl 1.5
2) TString exists in both Delphi and Free Pascal , so you can use TStrings OK.
3) SDL has it's own input system which under the hood under windows probably used dXInput, so I would stick with that. JEDI-SDL comes with an excellent input manager already SDLInput.pas
4) SDL_Image is good, but it depends on what image formats you want to support, I use SDL_Image in my engines.
5) I would abstract your physics interface in such a way that it doesn't matter, but newton has more support.
6) GLSL is supported by ATI and Nvidia so I would stick with that. I'm not sure if ATI supports Cg.

Hope this helps

I look foward to seeing you new engine is action, A3Dngine was great. BTW the SDL conversion of that engine is still available in the jedi-sdl cvs. So it you want to have a look at how I converted stuff to work with SDL feel free

Dean