QuickBooks Desktop was easier since there were just two of us, but we should have probably used the online version. We both travel all the time, which makes the desktop version a pain. Quickbooks is a very robust system, but it's not user-friendly when you want to do analytics and analysis.
We really don't use anything to supplement Google Analytics, other than what we do on social media, which includes Hootesuite, and reporting from FB and Twitter to track what was going on. For us, the main concern was trying to figure out where our customers were coming from. We have some online presence, but the goal was to build out a brick-and-mortar business. We were really concerned with where traffic was coming from and what regions it was coming from. We also work with a lot of bloggers to get the word out, so we wanted to make sure we were getting our money’s worth. We wanted to make sure that traffic was coming to our site directly from them.
We used to use PayPal when we didn't integrate through Weebly, our web-hosting service (Weebly didn't have an online store feature when we built our site). We also used PayPal because we wanted to do online international ordering. We later scaled back down and switched over to Stripe completely because that's what Weebly uses.
We started with MailChimp and never stopped. They had a free service, and when we were doing our research, they seemed the easiest to get set up and start using right away. I also liked their templates. I remember a friend recommended MailChimp to us, and for a long while our email list was small enough that we could keep using the free version.
We tried Google Drive at first, but I really hated editing in Google Drive. I found it all very cumbersome, and when we switched over to Dropbox, it just worked better. They’re also generous with space, so we don't pay for it.