Drachenschorsch - No issue running firmer springs on the front. If that setup works for you, then that's the right set up for your track. I do recommend you try other setups too as there might be a better setup, or just to reinforce your current setup is good.

My M03 and M05 both have firmer springs on the front too. The weight transfer is crazy while off-throttle and entering a turn. Hard to keep the rear from stepping out unless I have very good traction on the rear tires. That is where I want to get away from... relying on tires so much. If the chassis can run well on soso-loose traction, then you got a really nice setup for bashing at home or at parking lots. For example, my M05 ProV2 is like this. Very good with even not so good traction.