Can you attach 1905A to Schedule C if you have W2 wages also?

You mean a 1095-A health insurance?  Yes.  You only enter it from the 1095-A. When you enter the 1095A there should be a box to check for self employment. If you enter the 1095-A and select the "Self-employed and bought a Marketplace plan" box, it will automatically include those premiums in the SE Health Insurance section. So you shouldn't enter it again on schedule C.

Self Employed health Insurance does not go directly on Schedule C so it will not reduce your Net Profit or self employment tax.

If it does exceed your net self-employment income it gets split automatically. An amount equal to your net self-employment income goes on Form 1040 Schedule 1, and the remainder gets added in to medical expenses on Schedule A.