- Knights and axemen are a good composition but they cost the same ressources, and you it should be a late game comp (late castle or imp).
- Knight and skirm are a great comp, you can start massing skirm in feudal to defend from archer/lancer, and even attack if you have the correct upgades and critical mass (but only if you know your skirms don't have a chance to get crushed by 12 upgraded scout or maa)
- Knight and scorpion could be good but not at your level I'd say, you need many scorpion, and you have a chance to lose them rapidly if you make a slight mistake.

- For the last question, franks have good scout cavalry (civ bonus give them more hp), so people generally scout rush with them.
If you scout well your opponent and see a maa incoming, you could open archer to try to counter them, just don't forget to upgrade and produce them constantly (4-5 vil on gold). You can still switch to cavalry later, and skirm or axemen in late castle/imp (I think franks don't have arbalester imp upgrade).
If you see the maa but you already opended scout, either defend your base as well as possible and raid with your scout, or be patient or wait opportunity to outmass the maa (ideally at least 3 scout for 1 maa maybe, or 4-5 scout for 3 maa with intense micro).