Should I attach a copy of the federal tax return when filing the NJ return via mail?

Yes. Only include the first 2 pages of your Federal 1040.

Is this still relevant for 2024's return, 6 years later? Desktop TT says W-2, 1099, W2-G.  Does that mean 1099-B , 1099-DIV etc?

Forms W-2, 1099 series, etc. should be attached if there is any withholding for your state on them.