Hi, as a guy with almost 20 years of experience in the field (~3000 gigs and counting) and running audio tutorial channel on youtube for about 10 years now, I’d suggest keeping it simple.
Even tho it might sound counter-intuitive... use less processing. That often fixes problems at the source. Just straight mic to preamp and hpf often gets you already 85% there. Then tackle the problems step by step.
Of course mic choice is crucial, but if you get any of the big brand mics, I’d go for the mic that the singer is most comfortable with. Aside from bleed amount, you can fix most problems in post processing.
If you are only handling FOH and not monitors too, then you don’t need to split the vocal tracks so that he gets the non-processed vocals to his wedges/in-ears.
You said you are already using Waves plugins, so you might want to make a chain that does all the heavy lifting and bring it with you to all the gigs.
Start the vocal chain with just Q10 or H-eq and start just by turning on the HPF. If the guy is a bass or a baritone (like me, and I do death metal style vocals too occasionally), you REALLY don’t need anything below 150hz. It might sound high, but trust me, it comes up a bit when you compress stuff. Then set a lowshelf band at 600hz (this again might sound high, but if you use SSL eq and set the freq to 100, it goes about as high in Q10). Then adjust the low shelf cut so that the top end and low end are in balance. If the mic used has a problem frequency, take it down but touch nothing else. Now you should have a basic sound that is 90% there. Harshness usually means there is too much 3-6k area, hard to say without hearing the situation in question. But if you turn down highshelf at 1khz, it should tame harshness a bit.
I forgot to mention to set the gain levels so that the ”normal” vocals are at decent level. This depends on the board and venue. If you are having problems getting the quiet parts up, tackle that first before squishing the vocals down. I’d try using the yellow fader on Waves MV2. But use it gently, usually halfway is already too much. It also has the red fader which I personally don’t like. If MV2 doesn’t get you the result you want, try using Rvox instead.
Now I’d put in a limiter. Not a compressor, but a limiter. For example L1. The goal of this is that you put the output fader down the same amount you pull the threshold down, so you don’t get a volume boost should only get gain reduction on the loudest parts, so the guy can have his dynamic range, but so that the audience won’t soil their pants when he deep throats the mic.
For de-esser use whatever you prefer, personally I like F6 or RDe-Esser in the band mode, but using the renessaince de-esser needs a frequency analyzer to pinpoint the frequency down.
Try that and let me know how it goes :-)