30k is not competative. if you play it like it's competative, you may as well play
40k space marines, and go buy
IA:1 (I think it's one) Beyond that:
Death guard's 'fluffy' choices are all good on the table top:
Mortarion had every troop trained for every role (barring the specialist options) so you should generally give every
tac squad extra
CCWs.
Since Mortarion was so fond of the 'well equipped infantryman' he loved dreadnoughts and saw them as the perfect infantry.
The Death Guard Legion fielded excessive numbers of cataphractii terminator armor, do with that as you will

.
A Death Guard Tactical squad was fielded in multiples of 7, the most common being a 21-man squad (the 21st man being an apothecary, who acted as a second field srgt.)
That's just some of the base Ideas on
DG, of course they used a lot of chem stuff and what not, but with what's in the Calth set, I would probably build something like this:
1 Praetor in Artificer (using the 'chaplain' run him as a praetor with plasma (or archeotech) and paragon blade (since they come in many sizes, the maul would be fine, or you could convert it up)
1 Centurion (Primus Medicae OR anything, really) in Terminator armor
1 Contemptor w/ Kheres & p. fist
5 Cataphractii terminators w/ fists & 1 H. Flamer
2 15-man Tactical squads
If you wanted to expand this I'd go with some MK III from
FW to bulk out your
tac squads, and then a few apothecaries, but if you are worried about cost I'd invest into 1-2 more calth sets. 3 being the 'perfect' number. Were you to get 3, a good final list would be something like:
1 Praetor in Artificer (or Terminator armor, if you convert one to have a Paragon blade), The Reaping RoW (no one can run, everyone has move through cover, and can buy rad grenades, heavy supports are now troops as well)
2 Centurions of any kind (I'd reccomend a siege breaker for this list and a medicae)
3 Contemptors, 1 w/
MM & fist, 2 w/ Kheres & fist (convert one to have 2 Kheres?)
10-man terminator w/ P. Fists, 2 H. Flamers
5-man terminator w/ Claws % H. Flamer
1-2 Apothecaries (using the chaplains in kit as stand ins)
20-man
tac squad w/ extra
CCW
20-man
tac squad w/ Extra
CCW
10-man flamer support squad
10-man Missile launcher heavy support squad
10-man Heavy bolter heavy support squad OR melta support squad
10-man vet. Tactical squad w/
MLs
10-man seeker squad, a few w/ combi weapons (you should be able to get 9/10 in here, more if you weapon swap one of the combi-melta's off of the Terminator
HQ)
It fits the
DG scheme fairly well, and should work okay on Tabletop.