[Help with a difficult choice?]

Late reply, but Dark Melee and Dark Armor tinted blue can be a great stand in for water based melee powers. 

[Help me build a natural stalker]

If you want a weapon vibe claws can work as well, there are blade options that look like punch daggers, predator arm blades, or a cestus. And I like claws much more than Ninja Blade or Dual Blades, and Staff on a stalker is lacking because you lose forms. 

[Kat with SR vs WP]

I would expect the SR to do more damage, as quickness will give you a recharge boost, and you should be at the softcap without DA you can skip it and have higher DPA attacks in your rotation. 

[Electric Melee - Endurance / Sleep Procs in Attacks]

I have used the sandman chance for self heal in IM on Frozen Aura and it turns into a mini dark regen there. It’s great on AOE but I don’t think it would be as dependable on A ST attack.

[Super Reflexes for a Tanker, yay or nay?]

I love SR with Dark Melee, the heal in Siphon Life and the End recovery in Dark Consumption really compensate for the weaknesses in SR, especially with the recent changes to buff the AoE on the set.  My main character on live was a DM/SR scrapper, I really need to get around to recreating it as a Tanker. 

[Sunsette's Guide to the Energy Blast Sentinel]

When reading over the Ice epic, slotting Frozen Aura with Call of the Sandman chance for Heal Self makes it a very reliable self heal while also adding to your aoe damage. I’d highly recommend it if you’re going Ice.

[DM/SR or DM/Ninjitsu?]

DM has less need for /Nins heal and endurance tools as it has both from the primary. SR is easier to hit the softcap and is really the only set that doesn’t have to worry about defense debuffs, and quickness makes it easier to perma hasten to have perma soul drain. To pair with DM, SR is the Bette rejoice between the two.