Hey there,long time no see bro.
First, you don't buy head amp....it is noisy and amp is not good for neighbors. if your house is cancel noise house it is not problem..but if you are normal house...you should play the instrument in your garage( I guess it is common way is in America.)
I guess you should buy Taishogoto because Taishogoto is easy than normal string instruments.
But I guess Taishogo is a little bit noisy even without amp....then it is a bit hard problem.
Erm I recommend to use guitar head amp then you can play without Amp then you can play the Taishogoto with your head phones。
And you should look up "VOX amPlug G2 AC30 Headphone Guitar Amp" in your browser. or watch the review video.
problem of sound is very complex, watch out to shooting from your neighbors.
At worth case, you should switch to midi keyboard....piano is not must play double hand instrument, you can play only melody even one hand....but if you want to play a lot of instruments...you have to pay a lot of money (maybe $300 or more)

Conclusion : Buy Taishogoto and "VOX amPlug G2 AC30 Headphone Guitar Amp".

That's it

I'm not sure where is. your ultimate goal but I hope your good instrument life, bye.