Welcome to the forum.
I also started with MC 2003, then to MC Pro 24 and on to SONAR Home Studio 6. I own SONAR X3, but haven't used it too much.
Make sure you hit the Apply button at the bottom of the User Control Panel so your pic will stick.
Should you use MIDI? That depends on whether you want to add instruments to a song that you don't own or know how to play.
Most of us use MIDI for drums, in my case because it would be hard to fit a drum kit in my 9' x 11' room, plus I'm not that good at drumming.
Orchestra instruments, synthesizers, organs, pianos, or ethnic instruments from all over the world can be added to your song if you want to.
You might want a piano in your song and 2 months later decide a harpsichord would work better. With MIDI, no need to hire another keyboardist to rerecord the piece, just change the patch (instrument sound) in the MIDI track pane.
Your timing is a little sloppy on the acoustic bass part in the bridge? Just use the staff view, piano roll view or event list view and edit the note data.
As far as recording level goes, it shouldn't go too far into the red (you mentioned visual impairment; can you see the meters?), and should peak at about -12 to -6 for a 24-bit input.
Which brings us to your computer and it's sound card.
Most of us use audio interfaces that support the ASIO driver mode, and Cakewalk recommends them, too. Just recording your audio performance with your mic shouldn't be a problem, but the more overdubbing you do, the more you will need to monitor the recording while singing/playing, and stock computer sound cards cannot deliver the kind of performance required for real-time monitoring while recording.
Anyway, just about everything you need to know is in the Help files, and we can try to answer any specific questions you have.
Good luck!