Hi,
My question is what accounts need to be setup for startup balances? there are three possibilities of implementing ERP
1. in between financial year
2. first day of financial year
3. New Business
can you give examples of these three to add opening balances or startup entries in journal/ledger?

Let me answer your question this way:
When you bring in a company into a running Oracle system, most of the accounts already exist. Some new accounts might have to be created to accommodate the new company.
Step 1- Decide if only opening balancing will be migrated or if historical data needs to be transferred as well. Usually opening balances are brought in as of the start of the year. For the remaining months, summarized (or detailed) activity is brought in.
For example if your calendar starts from Jan and you are integrating a new company in Mar-12, you will bring in the opening balances as of Dec-11 and will bring in the summarized or detailed activity for Jan-12 till Mar-12. Data could be migrated using journals (ADI or manual) or interface table.
Step 2 - Accountants create mapping between legacy accounts and new accounts
Step 3 - Create new accounts/segment values if required.
Step 4- Migrate the balances and data in Test system
Step 5- Run parallel testing from old and new system
Step 6- Repeat the process in Production

(You have to analyze the impact of a new company on all components like Mass Allocations, CV rules, FSG Reports etc).