We plan to purchase PC+ and start using it.
In case we do setup in March and start entering contributions for April.
May we enter the Jan to March contributions at our pace, so we will not be too stress out?
Our fiscal year is the same as calendar year.
You've already accounted for the contributions in your accounts, that is, previous contributions have been deposited and the money used in the mission of the church. So, you really don't need to worry about the Funds Accounting side of the house.
So, from the time you start accounting in March when you entered your starting balances, you should then do all your contributions in Powerchurch then post them directly to Funds Accounting. This will take care of the income transactions for the future.
For the past, you can enter them at your leisure, just do NOT post them to Funds Accounting. Use the posting option of Only Update the Contributions Module. This will not create new transactions for Funds Accounting, and the Contributions module will be updated.