1. Magic - At first glance you may think they lack magic, but with your list (untouched by any comments I might make) you'd be casting 4 spells per turn.  Note that each of these spells automatically casts regardless of the power dice you roll.  The dice are simply there so your opponent knows how hard things will be to dispel.

Okay, now the list...

Why groups of 12 archers?  I'd just go with the basic 10 and leave it at that.  12 spread out just make the units more cumbersome unless you play with lots of hills.

Tomb Kings Cavalry are generally not worth the points spent on them.  Cavalry usually do good in other armies because of their better than usual armor saves and quick movement and Tomb Kings really can't take advantage of either.  Armor 4+ for units of 8 Cav will mean they will end up as pincushions really fast.  If you want fast moving then stick with 1 unit of cav and gor for chariots and/or carrion.  Also, in general Champion units for basic skellies aren't worth the points.  you are just opening them up to being mauled by a character through a challenge (this can be lifted if you plan on putting a combat oreinted character in the unit).

I'm curious as to what role the tomb swarms will play in this list?  Most people use them as a speed bump they put in front of large units of skellies and Tomb Guard but you don't have any big slow moving infantry to worry about.

While Enkil's Kanopi is a very useful item, its also highly situational.  Unless you are facing armies with lots of "Remains in Play Spells" I'd suggest using the hieratic jar instead.  It gives you that extra chance to make sure you get off that critical incantation.

If you are going to put your Tomb King in a chariot I'd highly recommend taking Golden Eye of Rah-Nutt.  Otherwise you may find him having to hoof it across the battlefield do to lucky artillery shots (there is no "Look out sir" rule since you need at least 5 rank and file).

Also, the Icon of the Sacred Eye is sort of wasted on the Chariot unit.  Impact hits don't need to roll, "to-hit" and the +1 doesn't affect the d3 roll for impact hits.

Lastly, I want to point out the lack of any backbone units like Tomb Guard.  One of the easiest ways for undead to win a combat is to win combat resolution and outnumber their opponents causing them to autobreak.  You don't have anything and are pretty much relying on first round combat resolutions because none of your units are meant for combat after the initial charge.

So, to sum up I'd make these changes...

Tomb King - Golden Eye of Rah-Nutt, Flail of Skulls, Chariot, Light Armor (288)

Remove Standard from Chariot unit

Replace Enkil's Kanopi with Hieratic Jar

Remove 2 Archers from each archer unit

Remove 1 Cav unit and Tomb Swarms and drop the champion from the cav unit you are keeping

Those trimmings would leave you plenty of points to eitehr buy a nice big unit of Tomb Guard (Highly suggested) or to buy whatever you think you need.

Tomb Swarms - I'm not sure they are necessary for anti-wartank given the Tomb Scorpion and number of archers present, but at least they serve a purpose.

Heavy Cav - Changes make perfect sense.  Personally I'd get rid of both units but I left one in before since its obvious you want to try them out.  Definately go to 10 for 7th edition.. good call.

Ushabti - They are absolute bears.  They will not break large units of concentrated infantry but they will tear through smaller, more specialized troops and are one of the few units that can withstand a cavalry charge in a Tomb Kings list.  Personally I'd go for Tomb Guard.. but then.. I love tomb guard.

As for your spare 35 pts.. I'd have more suggestions if I had my book in front of me.. but what about the Banner of the Undying Legion for your cavalry or 2nd chariot unit or it you go tomb guard definately get the icon of rakaph (can't remember points cost but its 35-40 or so).  ALternitively both suggestions for the points are good ideas... just remember the points limit for magic items (100 for lord 50 for heroes).

I'd love to see the final list when you are done tweaking it.  While I don't play my TK much anymore (largely because newer players often can't muster 2000 pts here).. They are still my favorite army.