Refrigerant volume/charge; receivers

Hello guys!

I need some information from You. I'm working on air handling units (AHU's) manufacture company. We are integrating refrigeration systems into AHU's. Refrigeration system will be filled with R410A. System will be capable of heating and cooling (4way reversible valve). Compressor, evaporator, condenser will be inside air handling unit and there will be short piping system (less than 10 meters). We will be using variable speed compressors. I've got several questions for you:

1) How to select suction accumulator?

My comments: I've found that the selection of suction accumulator must consider that the capacity of the refrigerant liquid must be at least within 50% of the total amount of the plant(that means according volume, correct?). Do you agree with that?

2) Difference between suction accumulator and surge drum?

My comments: I actually tought that surge drum and suction accumulator is the same thing only with other title, like suction receiver or something like that.

3) How to select liquid receiver?

My comments: I've found that the liquid receiver is normally sized to provide a volume to equal to approximately 125% of the total system charge (that means according volume, correct?). Do you agree with that?

4) How to determine refrigeration volume in the system?

My comments: For my understanding I should sum evaporator, condenser, piping volumes, correct? What about other components like filter-drier, sight glass and so on, I mean not evaluate it?

5) How to determine system refrigerant charge?

My comments: I've been reading that refrigerant charge can be calculated according to each component volume multiplying by refrigerant density at that point, is it correct? If it's correct how many points should be taken into account?
Also, I've found defra refrigerant charge calculator, what do you think about using it?

6) How to properly select filter-drier?

My comments: I'm looking through filter-drier catalogue. Filter-dier can be selected according drying capacity or liquid capacity. How to determine one or other value?

I know that it's a lot of questions from my side, but I'll be grateful for any information. The reason why I'm asking for all this stuff is that we want to make automatically prices calculation algorithm that could evaluate moreover all components (where is possible) and provide final price of such application.

Thank you for your answers in advance. If you need any additional information, please write and I'll try to provide it!