[neferhet]

The lord could be better served with fist + claw, he reroll to wound and gets +1 attack...
Then i'd drop daemonheart, powersword and plasmapistol from chosen champion, dropa another 5 demonettes and add as many spawns you can to escort the lord. Or bikers with meltaguns, if you prefer (4 spawns or 4 bikers with 2 meltaguns & combimelta with those points...).
Also,those dreadclaw chosen are...extremely costly. I'd be more happy with 3 units of 3 terminators with combiplasma for a total of 336 pts. But i can understand you, 'cause the claw model is extra cool

 

[neferhet]

Can you think of a way tactically to use 5 chosen with plasma?

In a friendly game, they are ok with the dreadclaw. A rhino is just worse. Normally, chosen stay put on the shelf. they simply have no reliable place in an army list.
I suggest you to try out the different capabilities of dread chsens and three units of termis. then you decide. Both options suck, btw :biggrin: Another fun, friendly option:
For the same cost you could take the deepstriking formation of 3 Helbrutes. add a plasma cannon and 2 heavy flamers to their weapons, and you have a pretty cool disruption group.