HOOOOOOOO BOY! LETS DIVE IN!
OKAY, so, first and foremost,
DG have quite a few super fluffy ways to build them up:
Infantry spam: LOTS of tactical marines, with LOTS of apothecaries, and LOTS of support/heavy support marines. This is SUPER fluffy, and with the right kit, works really well. ALWAYS give extra
CCWs (a huge part of the
DG battle doctrine was being well equipped to do basically anything)
terminator spam: we had the most cataphractii, and both of out legion special units are in terminator armour (and are damn amazing) with unlimited points, we can bring ~163 terminators
deadnought spam: Morty loves his dreadnoughts, and he saw them as the perfect infantry, spam 'em for a good laugh.
chem spam: CHem flamers, phosphex, and heavy artillery are all fluffy for
DG.
Our grave wardens are arguably the best unit in the game (amazing gun, take away charge bonuses, cataphractii armour, can over watch with the deathcloud, same price as regular terminators), and the deathshoud are one of the better beatstick squads in the game.
our rights of war let you spam rad grenades or give everyone stealth from a distance, which is cool.
Morty is an amazing primarch who hits hard, hugely buffs our army, and is the fastest primarch (6" move, 10" warp and can charge afterwards) and one of the shootiest (great pistol, unlimited long range phosphex bombs)
one of the single most fluffy units for the
DG are a 20-man
tac squad with extra
CCWs and an apothecary (21 being a multiple of 7 and what not)
as for how you should start out:
1) the first and most important thing with 30k is that basically every option is good and has a use. in my oppinion there is a single "bad" thing in the entire list, and that's rotor cannons, they make me weep :(
2) with 2
BaC you're at a cool spot. (though, if you have the funds, go for a prospero box since
DG LOVED MK III armour) something like this as a core start with let you expand a lot of directions and be fun to play as
DG:
1 praetor (any
HQ model, though if you could find a way to give him a paragon blade, thats probably best. I run mine with fist + blade in artificer armour)
2 Centurions of any kind (the "chaplain" from calth can be anything, he is in no way modeled to ONLY be a chaplain, same goes for the terminator praetor)
2 20-man tactical squads w/ extra
CCWs and Artificer on the Srgt.
1 5-man flamer support squad
1 10-man cataphractii squad w/ fists and combi-bolters. I give mine flamers for fluff, since you can't over watch
contemptor dreadnought w/ kehres + fist (you COULD build one as dual kheres, and then dual fists if you had the patience)
contemptor dreadnought w/ kehres + fist
1 5-man missile launcher heavy support squad
this is a solid core to expand from, and leaves you with 10 men to make apothecaries, vets, or anything else