I've read somewhere that 20% of your paying users use up 90% of your resources (support, app usage).
Does this hold true for your industry? In the past when I used to run a SaaS with an unlimited monthly plan, I saw somewhere around < 10% of the users were very active, racking up most of the bills and support requests while the rest would be more sporadic.
The people that used it were usually the ones responsible for selling the idea to their company. I suspect that it was often a way to be able to boast increasing company performance so they could use it at a performance review or something. This was at a time when money was being thrown around like crazy in the VC world and they were all spending money like it was nothing.
The Pareto distribution in customers is probably very common in general. I'd just make sure you have good metrics/monitoring so you can see usage trends and make adjustments and optimizations appropriately. If the math works that you can offer it as such, that's great. The most expensive thing (probably money and time wise) is support. Some customers just need a lot more support than others. Sometimes for good reasons, sometimes not. Getting an idea of the common support requests and making sure they're easy to fulfill or having a pre-canned answer/FAQ is a good way to reduce that.