Moving off a spreadsheet without losing history
You do not need to re-capture three years of transactions. You need a clean opening balance and a date you commit to.
The most common reason a migration stalls is the belief that everything must come across. It does not. Your spreadsheet remains your history; the new system needs a starting position and everything after it.
Pick the date first
The first day of a financial period — ideally your year end, otherwise the first of a month. Everything before that date stays where it is. Everything after gets captured properly.
What has to come across
Four things: your chart of accounts, your customers and suppliers, your unpaid invoices and bills at that date, and your bank balance at that date. That is the whole list.
Prove it before you trade
Your opening debtors must equal the sum of unpaid invoices you loaded. Your opening bank must equal the statement. If those two agree, your opening trial balance will balance and you can start with confidence.
Keep the old file
Do not delete the spreadsheet. Archive it read-only. If a question about last year comes up, you want the answer available — you just never want to work in it again.