small AV installation company in need of invoicing

QUICKBOOKS

its the industry leader that most bookkeepers use and also easiest to learn and use for owner newbies. It has an on-line version that permits you to use it in the go. 

(I’m a CPA)

I do some consulting on the side.  For simple invoices I use a template in Excel.

@akg_ca +1, Quickbooks. Especially if you hope the business will do well, it can handle small to medium size businesses with no problem. And being online, it's always available wherever you are and is backed-up automatically. 

i use Invoice24 with my company, i found that compared to the other ones it's the least complicated and easiest to use and it's free unlike most of them, here's the link if you wanna check it out, https://i24app.com/ hope you find one that works best for you🙂