These are my 3 key things to consider
I often get asked about gear and talk to people about what gear they have and which is better X or Y. There are lots of great sounding gear and many people on award winning shows all use different types of equipment.
1 - Buy Decent Wireless Last, Start with G3s.
So many people ask me about my Lectrosonics or any other of the great companies of high end wireless systems but don't have a hypercardioid yet. Before wireless (Transmitters, Receivers, Headsets, Slates etc..) you should have Mixer/Recorder, Shotgun, Backup Shotgun (416) Hypercardioid mic, Boom Poles, Mics like Sanken COS-11, DPA 4061 for your Sennheiser G3s.
I say start with Sennheiser G3s because for the value they are fine but make sure you buy a few last and get everything else in order first before upgrading for wireless transmitters.
2 - Buy Once, Cry Once. After Testing Of Course.
Ideally you want to upgrade to the highest quality gear (Usually the more expensive) in as fewer steps as possible to be able to maximise the value for money and not lose anything on investments in between, the faster you can get to the best gear you want and have tested essentially the better, don't be tempted by short term gains. Note I Put This Second: If you haven't upgraded the core gear first then afterwards upgrade the wireless systems.
3 - Does It Make The Recording Sound Better Or Easier?
The most important thing is the end result being the sound quality, gear is only a small but still critical part in this. Your choices in gear are to make the "sound" better or easier to record. This is why you should invest in the core of boom mics and a mixer / recorder that will make both the job easier and the recording better. Asking yourself if this piece of gear is making the recording better or easier?