How many rows ?

Excel XP has 65,535 rows.
Excel later than XP has 1,036,000 rows.

Estimated, a one year transactions require how many rows ?

Sales invoices :  5 invoices per day X 300 working days X 2 rows = 3,000 rows.
Debit/Credit Notes : 2 per month X 12 months X 2 rows = 48 rows.
Supplier invoices : 10 invoices per day X 300 working days X 2 rows = 6,000 rows.
Journals : 100 per year X 2 rows = 200 rows
Cash/bank transactions : 200 per month X 12 months X 2 rows = 4,800 rows.

Total = 14,048 rows.

So, one Excel XP sheet can easily accomodate a one whole year transactions, and occupies only about 20 % of the space.