FICO Data Conversions clarifications

Hi,

I am currently working on data conversion project. We have our FY from April to March and we are going live on June 01. I am trying to analyse the FICO objects. I have seen many conversations here but confused between balances and open items. I am trying to use ABAP programs instead of LSMW as much as possible

Master Data:

1) GL Master Data

2) AP Vendor Master Data

3) AR Customer Master Data

4) FA Master Data

5) Cost Centers

6) Profit Centers

Transaction Data:

Note that client wants to use only one offsetting conversion account instead of one account each for GL, AP, AR, FA etc

7) GL Balances

what is the difference between balances and open items here and how do we post them (can i use f-02 for both) and document types?

lets say i have GL 600100 which has a balance of $5000. If i want to post it during data conversion, should i post it as Dr 600100 Cr 700100 (this is a offsetting account used only for conversion)

how do you post an GL Open Items and what would be the accounting entries

8) Vendor Balances

what is the difference between Vendor balances and Vendor Open items.

lets say if i have 10 invoices pending payment for a vendor 10000, is the posting to KR doc type as Cr 10000 (vendor) Dr 700100 (this is a offsetting account used only for conversion) correct?

9) Customer Balances

what is the difference between Customer balances and Customer Open items.

lets say if i have 10 invoices pending payment by a customer 80000, is the posting to DR doc type as Dr 80000 (Customer) Cr 700100 (this is a offsetting account used only for conversion) correct?

10) Historical Data

If the client asks us to post data from April 1 until May 31, what is the best approach, also here we are circumventing few things such as

If there is a GR is done but not Invoiced, then these will be just posted as regular invoices (KR) instead of PO - GR - IV sequence

If there is Invoice (PO based ones) but not paid, then these will be considered as regular open invoices (KR) as above

like wise for O2C invoices too

I am trying to understand if i missing anything and if i have to follow any sequence. Appreciate if you guys can help with an example and if if i am missing any objects here...

Thanks

Shriya