The first step is to decide what you want from your list, then make your list on paper. If you have to take some borrowed figures and play with the proxies for a bit to get a feel for the game and your first list. then make purchases I did list a couple of safe ones a bit down the post though if you are a bit antsy to get started. We all where.

Tip on Ghost/Doomsday ark would be not to put the warriors on it and magnetize the gun. Don’t worry which facing the horseshoes are facing. ON the ghost ark they are up and surrounding the warriors that it is transporting on the doomsday ark they are down guarding the gun. If you always have them up and mod/magnetize the gun you can remove the gun when you want it to be an empty troop transport ghost ark, or put the gun back when you use it as a doomsday ark.

If you are looking for something to purchase right away, I would look into a couple of night scythes and magnetize them as well. You will probably want fliers, so they are safe purchases. There is allot of good things in the Necron codex so many purchases will seem good but not all of them will form a great synergy for your specific strategy. The fliers are going to be a strong part of any list going into forth so get these or look at building a Necron style defense line and quad gun.

For looking at lists really take a close look at the royal court for your overlord. most players use them and I don’t disagree with that. also go to forums like bell of lost souls and dakka dakka and look at other peoples lists and comment to see what appeals to you.

Red

Personally I’m really liking nightscythes for troop transports (getting them across the field in no time and bringing a tesla destructor are good things) and Doomscythes for their ludicrous damage output now that they are proper flyers with the ability to actually live past the first kill. Now I wouldn’t make a whole army out of them as I believe you lose if on any one of your turns you have no models on the field after reserve rolls. I suppose you could leave a single squad out but that’s dangerous if you can’t find really good cover. They are however hard to deal with in the current meta and have some pretty good abilities.
Oh and Immortal squads with tesla are amazing for overwatch.