The Form 8949 can be E-filed with your tax return. There isn't a "maximum" file size that can be E-filed (that I can find or have encountered). If the form is accepted for E-file, then the number of transactions shouldn't eliminate it from E-file. The IRS does request this Form to be mailed in many cases, but not all.
You can choose to separate long term versus short term activity, then make
two entries, one for each. Long term holding period is more than
one year. Then you can attach your
excel sheet (or other tracking sheet) for the necessary backup to your tax return entries. This an be mailed to the IRS with Form 8949 after E-file acceptance or if requested by them later.
