That's correct. You buy an auto-transformer to drop the voltage down - often the rating is in VA, just multiply this by 0.7 to convert to watts.
Might be easiest to grab one when you go over - they're readily available in most countries with 'real' voltages
because we're used to North Americans coming over and not realising that not everyone is the same as them
. You'll know you'll get the right plug then - although if you get one with an IEC inlet then you'll be ok. They are also very heavy in the rating you're talking about. Heavy = expensive freight!
It depends on the gear. Many older units I've seen (including my Akai and Ferrograph) use the mains frequency to control the speed of the motor. Running at a different frequency means a different speed. In the case of your machine it would pay to research this - often there could be a two-step (as in the Akai GXC46D cassette deck) or different size pully if its belt driven. If its direct drive look for a frequency control somewhere in the drive circuitry (my GX265D). In the worst case (probably unlikely in your Teacs but the case with my Ferrograph) there may have been a different motor used for each frequency.
If you do get stuck, then one way around it - unfortunately an expensive one - would be to use an inverter. This converts DC to AC - the idea being that you'd charge a 12 volt car battery from 230v/50Hz and then use an inverter connected to the battery to generate 120v/60Hz. Not an ideal solution, and if you run the recorder a lot you'd need a huge battery, huge charger or both.
The other possibility - and this is probably the case with the cassette-based Portastudios and certainly anything that uses a DC adapter or batteries - is that the motor runs on DC and that the DC voltage determines it speed. In this case frequency should not be a problem.
Now to the mixers. Any mixer I've seen uses a linear power supply to generate a range of DC voltages to power the rest of the system. There should be no problems running these on the 120v/50Hz you'd get out of a step-down autotransformer.
One thing that you'll need to get used to listening for is the 50Hz (induction) or 100Hz (poor smoothing) hums that we're all used to in 50Hz land. It will probably be more obvious, in the same way that 60Hz/120Hz sounds so odd to me!
Hope this helps!
Cya
Andrew