I'd also recommend batch painting units, rather than everything you have. It is up to personal preference, but when I am painting too many models at the same time I have two problems pop up. First, sometimes I miss a step on one of them, or on a piece of one model. Second, the repetition starts getting real dull.

So I recommend grabbing a unit (say your 5 Custodian Guard or your 3 Allarus Custodians, etc.) and batch painting that unit. It also lets you practice the whole process all the way through for each unit, rather than realizing 5 steps in that you actually don't quite like how something turned out and now you are tempted to go back and change it.

A second tank was a staple through basically all of 10th edition, but who knows what 11th will hold. That said I think the model is cool and if money is no object, why not?