I don’t have the codex in front of me right now (at work) so won’t be able to recommend specifics, but here are some comments on your list:
1. For assaulty armies (I play Deathwing as well), it is generally a bad idea to just “walk” up the field, you will generally get shot to pieces before making it to combat. Specially nurgle units, which are slow and purposeful (i.e. no running).
2. For getting your assault units up field I would recommend deep striking them, make sure you give an Icon to your Plague Drones to help prevent scattering. If you are deepstriking 10 man units, the footprint may be large enough that you may end up with a mishap. Also you may want to give Instruments to other units you may want to deepstrike to make sure that you have more than 1 unit arriving from reserves (you want to avoid just having one unit show up from reserve per turn).
3. I see nurglings as potentially good distraction unit. Since you can’t charge from deep strike, you can use your nurglings to infiltrate out of
LOS and then when your units arrive from deepstrike you charge the enemy with your nurglings so that they can’t fire at your assault units that just came into the game. The nurgling will probably die, but that’s ok.
4. Also for your offensive troop choice, I would not use the
PBs, instead look at either Daemonettes or Bloodletters, they are way more killy than the
PBs.
PBs are great at holding objectives… unless you are up against Tau and their ignore cover shenanigans.
I have not explored using the
GUO or the Cavalcade, so can’t really comment on either. Hope this helps man!