Stop thinking about it and set it up. There isn't anything to think about. Nagios (I like using it through groundwork) are certainly not overkill... it's think

Stop thinking about it and set it up. There isn't anything to think about. Nagios (I like using it through groundwork) are certainly not overkill... it's thinking like that that is what gets you in trouble in the first place. Get that tool in place NOW while you are small, so it's there when you get bigger... so you can hire people to watch it while you move on to other things. You will always have a lack of time, and always be busy. Spend a weekend putting up Nagios, setting up alerts over SMS or XMPP or Twitter or whatever you want, and then move on. This is fundamental to systems management. Dont' over think it - just get nagios/cacti (again, try groundwork) up and running and graph EVERYTHING you can... yuo'll be very, very glad you did.