The stretched part wasn't so much of can they use all of their abilities at one time as what I would consider someone of that level able to do with their class.

My math logic was basically this....
OK, that all checks out actually, so I have a suggestion (yes, another one!) for the hands. Put this at the top of the abilities section, right after Telekinesis:

Hands:(Su)
The Telekineticist has a limited number of hands equal to the number listed on the above table plus your Constitution bonus (so a level 1 Telekineticist with 15 Constitution would have 3 hands). Any hand which is used for a non-sustained ability is considered used until the start of your next turn.

This should negate the need for the changes you mentioned here:
My suggestion was that at 20, the final ability replace it's last line that makes each hand count for double for purposes of manual dexterity with Mental Strength, with one that reads "The amount of hands granted from this class double." Then at level 20 he really becomes the master of TK. He wouldn't really need all those hands all the time, but it would make it possible to wall off the enemies, make it hurt, have enough weapons in the air to be terrifying, and still carry the party/enemies around the field.
Should give you enough hands to do everything, but still have to think about it a fair bit. The feat I presented would thusly become less vital but still just as nice, and speaking of that feat...
If only takeable once, it should say so, just to avoid any misconceptions.
Look Ma, more hands!(General)
Requirements: Telekineticist 1st level only.
Benefit: For some reason, you have more hands than other Telekineticists, maybe you're just greedy like that...
You have extra hands equal to 1/5 Telekineticist levels (minimum of 1) in addition to the number listed on the Telekineticist class table.
Special: This feat may only be taken once and only at 1st character level.

I think that's better...

Still need clarification about how many hands can be applied to one instance of force blast...i.e. I take my standard action, and fling 7 heavy rocks at you! (Potentially at level 20) Take 280d6! Also, is there a minimum of how far the rock must fly? Or can it be launched point blank for all potential damage?
So perhaps an amendment to Force Blast replacing these bits...
As a standard action, the Telekineticist can launch an object within his telekinesis range, weighing no more than 25lb/level. The object travels up to 10ft/level and this movement may take it outside of your telekinesis range. The Telekineticist makes a standard ranged attack with the object, which deals bludgeoning or piercing damage...

...You may also focus this power as a blast of pure force. Doing so requires a standard ranged attack which deals 1d4/2 class levels force damage to one target within your telekinesis range. The target gets a fortitude save for half damage (this affects objects).
...with something like...

As a standard action, the Telekineticist can launch a number of objects within his telekinesis range equal to the number of available hands he wishes to use. Each object may weigh no more than 25lb/level. The object/s travel up to 10ft/level and this movement may take it outside of your telekinesis range. The Telekineticist makes a single standard ranged attack (in the case of multiple targets, this result is applied to each target seperately), with a -2 penalty for each object thrown beyond the first, which deals bludgeoning or piercing damage...

You may also focus this power as blasts of pure force. Doing so works just like throwing object/s, except it requires no projectile, deals 1D4/2 class levels force damage and only functions within your telekinesis range. The target gets a fortitude save for half damage (this affects objects).

I think that covers everything, hehehe!