Please could you people suggest to me some general tactical/stratagy ideas for the following 1500 IG list, when facing all sorts of unknown opponants (that will defo include lots of space marines)

[please note the list wont be changing, as these are the models I have ]

1x primaris psyker joining
1x vetrans squad with a vox and 2x meltaguns
in 1x valkyrie with multilaser and missle pods

1x infantry platoon consisiting of
1x platoon command squad with
officer w/ power fist, vox, medic, 2x grenade launchers and commisar w/ power fist
in a valkyrie* with a lascannon and heavy bolters (and hellstrikes)

1x squad with vox, melta and commisar w/ power sword and plasma pistol
in a valkyrie* with a lascannon and heavy bolters (and hellstrikes)

1x primaris psyker joining
1x squad with vox, melta and commisar w/ power sword and plasma pistol
in a valkyrie with a heavy bolters (and hellstrikes)

* valkyries in a squadron

and finally

2x Squads of 10 Storm troopers... each squad 1x grenade launcher, 1x flamer and sarg has a power sword


Key things I am wondering:

I am thinking the best use of the valkyries is to play "fly away from the nasty power armour whist shooting them" then drop the squads on objectives as late in the game as possible... but is this a good idea

WHat is the best way to use the storm troopers?
My heart says "DEEP STRIKE" but my head says "infiltrate use them to harrass"... or any other ideas?