For a small business, a service such as GoogleApps or Microsoft365 is likely going to be a cheaper solution than self hosting this. Plus including productivity applications and cloud storage as part of the package in most instances.
It will be much, much safer as well. If you’re unsure of how to do this, do not do it yourself. Setup a home lab, sure. Use it to learn but do not run your business this way!
Source: Am e-mail admin.
I rate ME bank, out of the banks my partner and I looked at they offered some of the better interest rates for us and they’ve been pretty good so far. Downside is there are no branches but AusPost has facilities to allow deposit and withdrawal iirc.