Two problems- doubled starter course, and nails.

Normal practice is to double the first course for consistent thickness,
avoiding gaps in coverage, whatever. You're talking adding a course
under that.

The existing shingles are nailed down, making it difficult :') to slip
shingles underneath.

Dunno what you mean by "weaving"- is there a valley?

New courses you're talking will start from bottom (I hope), and you're
hoping that x courses will sync with the existing. Maybe.

Do you want this to look good, or like an obvious cheapie job? The old
shingles will _not_ match the new.

Not being a pro, nor Holiday Inn Express resident, I can see a real
mess, and redo, in the offing. IOW, I'd tear the old off.

HTH,
J