How many people can you transport and how do you use move and attack effectively?

Helps to quote the abilities. It helps eliminate confusion and a second read through can often reveal the answers. From the PG:

Carry
When moving as a result of being given an action, this character may carry one friendly character. When this ability is used, modify this character's speed value by –2 until the end of the action. Only characters with a combination of the following symbols can be carried: , , , , , , :g-staburst:. If a character has any other combat symbols or is holding an object it cannot be carried. To be carried, the friendly character must be adjacent to this character at the beginning of this character's action. When this character ends its movement for the action, the carried character must be placed in a square adjacent to this character. While being carried, a carried character is not adjacent to any character nor can it draw a line of fire until placed at the end of this character's movement for the action. A character which has been carried this turn can't be given an action (other than a free action) until the beginning of the next turn.

So a Transporter could carry one character.

Move and Attack
This character can use Hypersonic Speed if it is not adjacent to an opposing character when given the power action, but its attack value is modified by -2.

Anything that would make HSS more effective thus makes Move and Attack more effective. Also, since there is a negative modifier to your AV when you use Move and Attack, anything that helps negate the negative modifier (like the Outsiders TA) would be useful. Finally, since this ability can't be used if your Transporter is adjacent to an opposing character, try to keep your Transporter back where it is harder for the opposition to reach him.

Thanks for the help.

Follow up question. Isn't it true that if you use the Hypersonic granted by the move and attack, along with the -2 modifier to attack, the figures range is NOT halved but kept at full?

It used to be that way. But if you read the current wording above, it doesn't say anything about full range. It's HSS as normal if you aren't adjacent to an opposing character.

It is not true. Their range is halved like other HSS users.

This was changed last year in the 2011 rules. Before that, under the Blackest Night rules, it wasn't halved.

For the best way to use Move and Attack effectively, check out the Outsiders team ability, which neatly disposes of that -2 to attack. New Outsiders coming in Batman! I'm so looking forward to them!