Thank you for the kind words.
To get the gems, you must kind of 'get inside' the crowd a bit and get surrounded, rather than trying to avoid the crowd and stay outside. You can blow a path forward through the enemies with the gun and the Shockwave will be a big help in not getting completely overwhelmed.
The game rewards risk taking by being close to the enemies and thus being close to the gems to collect them as they drop before they expire. I guarantee you that you will have more than enough gems for 4 upgrades - including two tier 2 upgrades if you want, but this is a bit harder.
There's also an easy difficulty setting in the Options that you can set before starting your run , which will get you started with 10 gems and more hit points.
Cheers :)