This is the question i get asked all the time and frankly its got so many different answers that I've decided to give you the best advice I can.
Stock plugins and free plugins will help you mix a record just fine. Period.
There are enough free plugins in the world covering the spectrum of high end plugins that are out that paying the money for a "specialty" plugin is just that. The records you hear are processed to the upper echelons of mixing to achieve a certain sound. Now this isn't always true but in the plugin world its pretty much the same with a lot more pieces. For example, to emulate a desk you would need the input/preamp, channel strip, all nuances of the board itself, output from the board and this still depends on the make model and when the board was built as well as up keep.
Which brings me to this statement, use as many plugins as you need to achieve the sound you want when mixing (read this statement as many times as you need to). Your stock plugins in your DAW are made to be clean and usable right out of the box for all your mixing needs. All DAW's come with a usable eq, a usable compressor and probably a usable gate. Now what you here on your favorite records are the culmination of different things to achieve a certain sound so automatically you shouldn't be looking to what your favorite engineer uses but what sound they are trying to achieve using said tool.
You need that kick to jump out at you? Use saturation, harmonic distortion, eq, compression, parallel processing and the good ole just turn up the fader technique. So now ask yourself, what kind of plugins do you need again? The obvious answer is the plugin(s) that help you achieve the results your looking for which by choice are whatever plugins you decide to use. Now I have some AMAZING free plugins from one of the greatest plugin creators of all time right here. I don't use them all the time but when I do its that magic ingredient that makes a meal "pop" aka the mix.
This plugin suite is completely free and best of all have some of the most amazing sounding plugins your downloading finger can click. Again this is to let you know that you don't need top of the line plugins to make top of the line music.
