Coming to London and need some feedback/advice on my strategy for getting from Heathrow to Camberwell:

*Arrive Heathrow at 12 noon.
*Get through Immigration/Customs
*Catch Heathrow Express to Paddington
*Walk/catch underground to Bayswater (to get Sim card)
*Catch Circle line to Victoria Underground
*Catch Southeastern to Denmark Hill
*Walk to Camberwell

Questions:
*any thoughts on how long it will take a non-EU passport to get through immigration/customs at that time of day?
*is it worth catching the underground between Paddington and Bayswater, bearing in mind I’ll have to work out how to get from the Paddington above ground to the underground, dragging a suitcase behind me; or would it be just as easy/quick to walk (I've had plenty of experience walking)?
*how long will it take me to sort an O2 sim?
*what time would estimate I’ll be arriving in Camberwell?

?