If your data in excel is in a 'flat' format it would be pretty easy to export the excel data as csv then read in the csv into AutoCAD to draw. Even if you did this as 'stage 1' of the development process as a proof of concept and then work out whether to automate this from Excel or AutoCAD, either way you will need to work with both API's but at least you'll have your drawing engine done and a workable solution :)
Mick, thanks for that link, it's a beauty. I'll add https://www.joelonsoftware.com/2009/09/23/the-duct-tape-programmer/
Also: Interfaces - yeah, what @dgorsman said, they are the loose coupling real-thing we always hear about so abstractedly.
Mick I'm with you. For something so simple I don't want to bloat my application with a library. You could simplify even more though.Code - C#: [Select]
return File.ReadAllLines(filename).Select(l => l.Split(',')).ToList();