Well I will take it as a per effect situation now that I've listened to some of the music examples in your signature.
Waves - If you buy anything Waves I would get the Musicians II bundle only to start out with. It has great Eq's, the compressors are easy to set and sound good, and has doubler which is a plugin I still use to this day to fatten up vocals. I personally own the Mercury Bundle but I like a lot of their newer things that aren't included in Gold. The 2 plugins that I would just watch for being on sale from AudioDeluxe that aren't in Musicians II but in Gold are H-Delay and H-Comp. Those 2 are really cool and fun to use plugins that I would recommend. Waves tune and the light version of tune are actually better at auto-tuning vocals than auto tune and is a good option if you need it. Remember that all waves stuff is free to try out and you don't need an ilok anymore so try it out.
Eq - Reaper's EQ is perfectly fine and can pretty much get you going. My favorite EQ is Fabfilter Pro-Q but I wouldn't say it sounds better necessarily but it's definitely my favorite and has some nice options. I wouldn't spend the money here if I were you.
Compression - This is the one where I would want a couple of flavors. I never use ReaComp, that doesn't mean it isn't just fine but I use certain things for certain sounds and like comps that have less control over everything. I would get something like the Rocket or an 1176 type of compression to inject a little excitement into your vocals. I would also get an SSL type compressor for my buss like "The Glue" because I love SSL type compression for this and it really does do a great job on the master buss.
Reverb / Delay - Everything Valhalla DSP does is great and I consider to be one of the best bang for the buck companies for VST's. You really can't go wrong with these and I have the most expensive options and still use these...they are great.
http://valhalladsp.com/
The other thing to do is to get the Bricasti M7 Impulse Responses and a stereo convolution reverb like reverberate because it is a good way to get damn good reverbs for not much money. I own a real Bricasti M7 hardware reverb and I can say they aren't the same but they are definitely in the direction and sound excellent. The M7 is by far my favorite option but it isn't a VST. My favorite VST delay is Sountoys Echoboy and my favorite VST reverb is the Lexicon PCM, UAD EMT 250, and the UAD Ocean Way which is one of the best room verbs I've ever heard. All of these are super expensive and probably wouldn't be the smartest things to start out on. PSP audioware also makes some really good easy to set delays but try them out and see if you like any of them.
Limiter - My favorite limiter is the Fab-filter Pro-L because I think it does the best job of making your mix louder without changing the sound of your mix. I haven't used and do not know of any option for a cheaper limiter. Fabfilter makes amazing stuff for sure. Izotope Ozone has a limiter that I think almost as good as Pro-L and has some other goodies on it also and does save you a bit of money.
Distortion - This is the one that I've been using a ton lately for compression and so many things. A lot of time I will use a distortion program over an eq to bring something to the front. A lot of times you don't hear the distortion but it does something cool to bring things out. Fab-Filter Saturn is one of my favorites, some of the softube ones are really cool...just look around. This is one I like to have options of because all do different things really well.
Find the vst's that work for you and make them work. Don't go insane with too many options and learn to make it work with what you have as opposed to getting too many options. You will learn more and become better at your job. Get inventive with your VST's and run delays/reverbs into compression and the distortions and then mix them in on a buss. Learn how to use your reverb and delays on busses for sure and use them on several instruments because it will glue your mixes together. Read and learn about studio techniques because technology is a cool thing and it is amazing that our $60 Reaper program destroys most of the options that our favorite bands of the 60's and 70's ever dreamed of.