Hi evildog, welcome to the Necrons.
I suggest you have a look at this thread :
http://www.dakkadakka.com/dakkaforum/posts/list/451042.page
which may give you some tips.
In respect of your current list, it doesn't synergise well, in particular perhaps the following comments will help:
a) Deathmarks are generally used with a Harbringer of despair with veil - this makes them a more powerful unit.
b) Lychguard are very slow unless they have a veil of darkness or Obyron. If you are planning on walking them, use wraiths instead.
c) small scarab swarms have some advantages (opponent can shoot at one or the other etc) but yours are too small
imho. Maybe 4, preferably 5. A lot depends on what you are going to do with them. If they are just hanging around as a screen for the warriors maybe 3 will do.
d) Doomsday ark - generally not a unit which is selected over anni barges unless you have stalkers in the list.
e) The C'Tan is commonly used with TremorTeks, maybe check out TremorTek lists/batreps to see if you like the principle of those
f) With the orb lords, your warrior units are sort of big enough to take some advantage of them. However, for the points, you might be better off getting Phaeron on your overlord and putting him with the gauss warrior squad (beef it up a little) and getting a ghost ark. Depends on how you want to play.
g) You are lacking Anti Tank (normally LanceTeks (Harbringers of Destruction with Eldritch lances)) help with that. 3 bases of scarabs in a squad aren't a big
AT threat.
Probably enough to think about, overall you have the models to take your army list in a couple of directions, question is which one you prefer to play.