You can totally DS the medusae in the Venom, that will not be a problem. I am not a huge fan of the Succubus. I understand what you want her to do, but I feel they will blow the venom and her up with it which will not take much to do. I would drop her and take a second CAD.
The second CAD can be lead by a Llahmaen and you can grab 2 of your troops you already have and put them in it. I would then grab a Fast Attack Venom for the Shadowseer. You will be glad they are in a transport for the extra protection and movement (if outflanking).
I would use the extra points for Dark lances on at least 2 of the Ravagers. If you have extra points, grab some Haywire grenades or another Medusae in the squad.
As an aside, I have found Haywire Blasters underwhelming so I personally would swap at least 1 squad for Heat Lances, if not both.