The chain length is fine, you KNOW that because the lower pulley still has room to swing upward. (Sram lower pulleys can swing above the lower loop even if it's dead straight, hence the big/big+1" minimum length).
No harm in working on bicycle upside down, the RD function isn't affected by gravity, and aero cable routing eliminates the damage to cables that used to be the issue.
However I wouldn't oil a chain with he bike upside down because dripping oil IS affected by gravity.
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