Building a HaloCastle - C/C requested

I've heard there's been some success with building something of a castle/gunline out of Haloscreed, and the idea of that appeals to me, so I'm trying to build up a list. I'm stuck on a few of the options though, and I know that some of my personal choices are vanity more than anything else.

Cawl (Warlord. I'd prefer to keep him just because I love the model, and Shroudpsalm is useful on a castle)

Datasmith + Wafers + 4 Fist/Fist/Blaster Bots

Engineseer

Manipulus + Ordinance + 6x Plasma Destroyers

Manipulus + Cognitive + 6x Arc Breachers

Rangers (full kit, Omni)

Rangers (full kit, Omni)

Vanguards (full kit, Omni)

Vanguards (full kit, Omni)

Dunecrawler

Dunecrawler

1980/2000

A few toughts:

Normally I like my Dunecrawlers with Neutrons, but I've heard the Arc Breachers might be enough firepower for anti-tank... would I use Phospher on the Crawlers instead for weight of fire?

I don't want to run boats... would the 4 battleline do the trick? should I perhaps drop something for scouts or infiltrators? I don't have enough leftover points for 2 Raiders or 2 Infiltrators.