Hi there ! I'm not a very experienced player yet but I know a bit of theory haha.
I take it you're planning to place the Techpriest among your Kataphrons to protect him and make them hard to kill. The Eradication Ray in this case is good to destroy Marines with its AP3, but I don't know if you'll hit loads of targets with the explosion, but in my few parts I noted that a BS5 is really good to mitigate the scattering. The Volkite Blaster is still quite good with 3 shots, but yes it'll allow them saves. Having a chance to double your wounds is still nice to consider, your choice.
Nothing to say about the Kataphrons, I made mine the same loadout
I don't know the rules about Knights so can't help here.
Now I see your Arc Rifles Rangers and wonder, do you plan on getting them that close ? You still have your Dunecrawlers to deal with tanks, and if I calculate right your 3 Arc Rifles cost you 45 pts. It just seems to me they'd be a priority target for the enemy, and Rangers ain't hard to kill sadly. But I'm no expert. Galvanic rifles should be really good against Eldars and not bad against Marines with S4. Love their range too.
4 Arquebii, now that looks like anti-tank material to me. You keep your distance and can reliably shoot down light armor in a few turns. Not sure if the Alpha is worth giving a Refractor field, is it the 5++ or the Blinding 4++ one ? The first is cheap and not dangerous, so ignore this comment if it's the 5++.
The Plasma Squad with preferred enemy, a load of points but really dangerous, I'd advise to run from cover to cover until in range because they're a juicy target. The Pater Radium might be nice to discourage an assault on them too.
As for the Dunecrawlers, do you have a lot of fliers at this point level ? I'm a bit stranger to fliers as of now. The Neutron Laser is tested and approved, I made a Triarch Stalker explode in one shot, killing two other Warriors in the process. Bonus for the Cognis Stubber who can be helpful against tarpits charging you.
Hope I helped with my humble opinion !