Setup for EV plus — amps

Hi there,
I’m new for theremin and currently building my setup. I’m professional musician and completely clueless when it comes to STEM… be patient please 😅 I’m doing my best!
I got Etherwave Plus (serial number 9000) and mic stand. I’ve just ordered also ESPE01 mod which friend of mine will install for me (engineer). 
The instrument needs calibration which I’m going to do but currently I’m struggling with amplification. I think I’ll go for monitor but not sure which one, and should I get one or a pair? I have opportunity to buy pair of Yamaha hs5 monitors in very good condition and price. Do you think they are suitable? I’m afraid they’ll be too loud for small venue (I’ll be practicing at home which is really tiny)…
I feel so lost in all this technic stuff around theremin, really hope you’ll help me!

Welcome to the madhouse 🙂.

If you're only playing at home and small venue, you can get away with a smaller speaker (I've tried and would recommend spark Mini and Sony xb21 or 31). I also have a monitor (Adam t5v) which is great and suitable for large venue (eg. Church size). 

It's a monophonic instrument, I don't think there's any benefit to having a pair of speakers. 

Feel free to update your TW profile to include your location, there could be other players around you that you're not aware of! 

Keyboard amps are pretty good for Theremin.  I use to split signal taking one channel into keyboard amp the other into bass amp. Very full sound.

A small powered monitor, keyboard amp or acoustic instruments amp are good for home practice and small venues. For home practice you also might consider a headphones amp. Guitar amps are less suited because of the high output level of the Etherwave theremin. 

Some suggestions: Behringer KXD12 or KXD15 Ultratone, Vox VX50KB (very lightweight), Roland CM-30 Cube Monitor, Roland KC-80, Behringer Eurolive B105D (small and light weight, can be mounted on a microphone stand, has built-in MP3 player and Bluetooth audio streaming for backing tracks), Boss Acoustic Singer Live LT, Hughes & Kettner ERA C.
 
It depends on the power supply that is with it how the theremin needs to be grounded, the USA model gives grounding through the power supply, while in Europe and I suppose other locations as well, the power supply doesn't provide grounding, so it expects grounding from the amplifier (or otherwise). 
Sometimes one can get away with just using a long cable between theremin and amp draped on de floor to provide enough earth grounding, when there is not too much electromagnetic interference around.