- Does this combo and fare apply during the week?

All the time except 2 to 4 AM.

- Is it fairly easy to take the bus/subway with a small amount of luggage (1-2 pieces)?

Two small pieces is easy. One big piece is not.

- Do you ask the bus driver for a transfer when you board the bus?

The bus driver can only give you a transfer to another bus. You need a Metrocard to transfer to the subway for free. Otherwise, pay $1.50 cash (coins only) and then another $1.50 at the subway station.

On the way back, buy a Metrocard with one ride in the subway station downtown and use it for the train and bus on the way back to LGA.