Many accounting systems are set up to run on a annual basis, and these are usually 'closed out' at the end of the year, and a 'new' year started with the ending balances of the previous year being carried forward. If this is the case, you (probably) should follow that practice and would have no issue with the number of records or database size.
If you are doing something else, ther may -at some point far away- be an issue. If the app adds 5K records permonth and you can handle 1M records, you have ~~ 200 months or approx 15+ years before the whistle blows. Given the pace of progress, it is somewhat doubtful that much of the process will remain static for that period of time, so the process changes will certainly impact the time scale (and probably in your favor).
My conclusion would be to borrow the tag line from Alfred E. Newman - What? Me Worry?
MichaelRed
m.red@att.net
There is never time to do it right but there is always time to do it over