Your #1 is grammatical, while your #2 is ungrammatical.
Your sentence examples are in the form of subject-dependent inversion. The subject has been inverted with a verb-phrase (VP). The subject is the expression "our compensation plan, an independent contract agreement, and a W9", and the VP is the phrase "attached".
This is your original version #1, with the subject and VP in brackets,
- [Attached] are [our compensation plan, an independent contract agreement, and a W9].
And the following is the corresponding non-inverted version, which has the subject first,
- [Our compensation plan, an independent contract agreement, and a W9] are [attached].
Here is some related info from CGEL, page 1385:
In subject-dependent inversion the subject occurs in postposed position while some other dependent of the verb is preposed. A considerable range of elements may invert with the subject in this way, as illustrated in :
 . . .
- iv. Arrested were Nathan Johnson, 23, of New York, and his brother, Victor Johnson, 32, a 15-year Army veteran.
. . . Complements in these examples are . . . and subjectless non-finite clauses, or VPs, in [iv-v].
Note that CGEL is the 2002 reference grammar by Huddleston and Pullum et al., The Cambridge Grammar of the English Language (CGEL).