The venue you will be performing can make a big difference in the way you monitor your rig. For instance, in a small intimate type of club, you may not have a choice but to bring your own monitor if the PA is only dedicated to vocals.
In mid sized rooms, you may have a suitable PA system, where you would be able to get by without a monitor system.
In Larger rooms, like most hotel grandballrooms, you should have both a stage monitor and a send to the house PA.
But, again, depends on how you will use it. Do you use patches that require a stereo mix such a B3 with leslie effect? or does your general sound get by in Mono?
This is kinda hard to answer as there is so much to consider. Personally, I have been giggin for over 20 years. I have used many different monitoring configurations. I have always sent a send to the house PA when possible. I started with a mini PA for my system, which consisted of a separate components like a 8 channel sub mixer, 400W amp, 18" 3way Cerwin Vega cabinet. This was sometimes louder than the main PA...Through the years, it only made sense to compact my stage setup. (1. I was not getting younger and everything seemed heavier. 2. I wanted to setup and breakdown within an hour or at least before the drummer.)
I only switched to a combo amp the last 2-3 years. I got a KC-550 to replace my mini PA, and even bought a second unit, the KC-350 for smaller venues. Honestly, I have not used my KC-550 for over a year now and have played some pretty big rooms. The KC-350 was plenty for my stage mix.
And yes, I am always set up and going home before the drummer now..........my rig consist of the Fantom X6, Roland RS-50, Roland A-37 and Roland AX-7, both controlling a Korg X5DR. With the KC-350 ease of set up, I now have more time to also set up a wireless midi system for the AX-7, and a wireless headset microphone. Most of the rhythm section is wireless as well as our horn section, so now, the WHOLE venue is our stage.
Good luck with your choices..