Best for the $$ is the Burton portable induction cooktop. Has both the highest "home" and Pro wattage for the price. About $70 for the 1800W home and $270 for the 220V 3000W. one on Amazon.
The home one should boil a quart in less than 3 min and the commercial version should be faster. A few Commercial list about 1.5 gal in 8 1/2 minutes, and that seems about right to me. We use the 1800W one about three times a day to heat a gallon of water (for other applications) in less than 10 minutes... However, if you never use all of the water in the kettle and it remains constantly hot, heating time will be even faster.
That's all i got.
I've used a variety of induction tops from the $100 home versions to the big pro versions. By far my favorite are the ones made by Cooktek. They're more expensive than most but certainly worth the money.
Speak to your local restaurant supplier, they usually will offer a considerable discount off of the MSRP.
I think you would do better to make the plunge and buy a tower right away. It's more efficient and also provides hot water for americanos without taking from your espresso machine's boiler.
And I encourage you to consider press pots instead of chemex. Although the chemex is clean and easy-going and brings a lot of flavour from a delicate light roast, IMHO I don't think it has the same funk, body and mouthfeel as a french press.
When you do get a water tower make sure it has a function to set the temperature. There's debate as to the perfect temps but between 195F and 206F is where most people end up.
I also have concerns about reheating water. My tea training tells me that water needs to be fresh, moving, alive and from as close to the source as possible. I know we all live somewhere that has treatment plants but try this: run the tap for 30 or 40 seconds then take that water that has run through your house's pipes and from the big pipe on the street where it is mixed with all that fast-moving water and prep it in the kettle for the chemex. Make tasting notes. Then 30 minutes later use the remainder of the kettle, re-heated and compare your tasting notes.
Ah well, maybe that's a conversation for another post.