Is it your first game ever???
if it is then , Just from my experience (and I still class my self as a noob) , I recommend having a good few weeks play with C2 to see what it does and how it works before you start adding 3rd party plugins and code. Then first make a few simple noob games to get all the big mistakes out of the way and, most importantly, test elements that you want to include in you game before you start real thing. Also get into the habit of organising your code in groups, and get familiar with functions, families and containers as they can save you a lot a time and aggravation down the line.
This way you wont be hundreds of lines of code in when you discover you have to start from scratch again because of some awkward way you implemented something that now needs to be changed. (This can really demoralise and possibly kill the whole game making dream - I have been there)
personally I would say that construct 2 gives you all the tools you need without 3rd party plugins
if you insist, though not free, there is a BulletML plugin available (which appears to be a standard requirement for bullet hell games these days) and also a pattern editor both in the scirra store for very very low prices
I still say you could probably do these things yourself once you get familiar with C2 though they may save you time.
however , code wise , in the forums and the tutorials you will find plenty of links to free plugins developed by forum members, and capx files and code examples for pretty much anything you will need. And if there isn't there is the healthy and friendly forum where you can ask.