I think it depends on your personal financial situation and what level of risk or confidence you have or are prepared to endure without detriment should things go pear shaped.
One thing's for sure, you do not need a big bank at all if you have a clear edge.
Compounding will build your bank quick enough.

__________________
RaceCensus - powerful system testing software.
Now with over 420,000 Metropolitan, Provincial and Country races!
http://www.propun.com.au/horse_raci...ng_systems.html
*RaceCensus now updated to 30/06/2025
Video overview of RaceCensus here:
http://www.youtube.com/watch?v=W821YP_b0Pg