a) Coming in from TPE to BKK, is one side better than the other for scenery?

b) Does BKK utilize dual boarding bridges for 747's?

Depending on which way you take off from TPE and which way you turn, you could get a view of central Taipei from either side. Just as likely, you'll take off heading westbound and won't see anything.

More often than not, aircraft land from north to south at Bangkok. To get any view of the city, you'd need to be on the right. But the city will be far away and you won't have much to see of interest. If you land from south to north, you won't see much of anything regardless of which side you're on.

b) Does BKK utilize dual boarding bridges for 747's?

Depending on your carrier, you might be using a bus for terminal transfers. Last time I checked, construction (re-construction) was continuing at Suvarnabhumi and some of the gates were not being used.

either side will be scenic, except for the part between Taiwan and Vietnam. Left side of the plane will be better if you're flight departs to the North from TPE. You'll make a left turn then have the entire Island to view out the left side. You'll enter Vietnam over DaNang. Scenery is good on both sides. As mentioned above, BKK will be off in the distance and with the haze/smog there, the city is pretty difficult to see most of the time.

Carrier is Eva (BR) if that helps.