To clarify: if i attack a territory and suffer greater losses than i expected i can move additional land units in during my movement phase to help defend it?
Yes that is right. So long as you won the battle you can move in further troops to defend it on your non-combat move. Aircraft, however are excluded as they must land in a territory that has been controlled by you or an ally since the beginning of your turn.
Also, a transport can not move then pick up a unit, the transport must start off in the same sea zone as the units it intends to load?
Actually a transport may move, pick up troops and either drop them off or move again and drop them off. Once a transport unloads though it must stay in that sea zone until the following turn.