newbie' 1500 all comers list, pure GK

Grandmaster Nemesis force weapon, Sacred Incense, hammerhand, psychic hood,
frags, targeter, psycannon 217

4x Terminator retinue 1 incinerator, 1 thunder hammer/storm shield, 199


9x PAGK 1 psycannon, justicar: meltabombs, targeter, frags 282
9x PAGK 1 psycannon, justicar: meltabombs, targeter, frags 282

Landraider Extra armour, smoke, dozer blade 263
Landraider Extra armour, smoke, dozer blade 263

1506 points

This is my first attempt at a 1500 all-comers list (I know, 6 points over but it'll get worked out eventually). I'm not too experienced with GK yet so let me know what you think. I hope this seems like an effective water warrior list. Not sure if maybe I should lump the psycannons into one squad or not.

Looks good. A third GK squad would be nice but I know it's hard to run 3 decent-sized ones when you also have two LR's. If you're planning on running one of the GK squads in an LR you might think about adding a 'cinnie. Just to let you know models in Termie armor cannot take frags or targeters so that saves 2 of the 6 points right there.

I like what you've got planned with your PAGK squads, very well rounded and equiped for just about any opposition (melta bombs for armor, frag for troop)

Since most of my stuff is on foot I give almost all of my justicars auspex incase of cowardly infiltrators and the targeters are a MUST!

That's a nice list. However, as stated above, if you want the knights in the land raider then an incinerator is really preferred above the psycannon. Either that or just keep them with stormbolters, they are also good, even one of the best infantry weapons in the game!
And another point, if your opponents are a bit annoying or really want to play like on tournaments or something, they will make a fuss about the extra points above the 1500...
Another option would be ofcourse to put the psycannons in one squad as you already said yourself, keep this squad as fire support and objective claimer for the objective in or near your deployment zone. Then you can use the landraiders for the terminators and the other squad of knights (preferably with an incinerator).