counting

1)I have 2 question about counting.
Is better to count when im alone against the dealer and i playing one hand or the table are full of people.
2)When i should raise my bet according to count ,could i replace it by hands instead of raising bet.
For example my minimum bet is 5$ in one hand and when count rises i do for example 2 5$ bet in two hands.Is there diffrence?
Thx for any advise