Thanks for the advice, I'll try that out tonight!

When you say Vlemish and then Plenor, do you mean that you'll sell the Vlemish and upgrade to Plenor? or have the Plenor in addition to the Vlemish?

Think of it this way - the lower your regen is, the better the flat rate is over a percentage.

Say if you have +10/s regen, adding a +10 regen item is effectively +100% regen, and using a 70% regen item in this case would only give you a +7.

But, if you have +20/s, adding +10 is only a 50% regen bonus, while a 70% regen item adds +14.

So the higher your base regen is, the more effective a percetage boost becomes over a flat value. The exact point at which a percentage becomes better would depend on a bunch of things (level, build, and whether it uses base regen or modified regen which I'm not sure about).

no real rule of thumb yet, but Vlemish is usually the first item I buy in this build.  I'll only add Plenor if I find myself running out of mana before a given fight is over, and your abilities shouldn't use too much mana til level 7 or so, depending on your DG and build...If you are really spell heavy you might want to consider one of the flat-rate mana items in the favor menu to start with...

Generally if I need that much mana I'll keep both items, because the % will stack on the flat rate. 

Sevenix did a nice chart progression of the DG stats in Beta 3, but the numbers won't apply anymore.  When someone technical and awesome makes one for this build you'll be able to chart precisely at what point it becomes more effective to go % for a given DG by level. 

On the bottom right of your Demigod's portrait is the Status button, it will show your equipped items and all the stats. You can hover over the health and energy numbers to see the exact regen rates for them.

Damage and attack speed and all that other good stuff is also shown there.

Until someone makes a spreadsheet though you have to check each one like that individually