Correct, the way a Reeves drive works is as one pulley gets bigger then other gets smaller and it works like gearing on a car or bike. It's a way to achieve mechanical speed control and keep costs down without having to add phase converters and use 3 phase motors. Make sure you follow the instructions on maintenance of the pulleys. These types of systems are common a lot of lathes, over time you could have some sticking where speed control isn't as smooth as it once was. Just keep up with the maintenance and you're good to go for many many years.
Yep, poplar will be much more stable than 2x4s for only a little more money.
Nobody here is advising you to not build the chair, only suggesting a little higher quality lumber to save you the headaches. Bench looks awesome!
Grab some poplar from Home Cheapo and build that Morris chair! Leg stock can be 3/4 stock glued up. If there is a will there is a way! If your inspired to build a chair...build that damn chair! Don't hold back for anyone. You have limited budget, that's fine. No power planer or jointer, who cares! Based on the photo of that bench YOU HAVE SKILLS and understand how to select wood!
CHOP,CHOP,CHOP.........JUST DO IT!
I absolutely know that woodworking is something that people take very seriously, and it should be. I also know that there are long-standing traditions, 99% of which are based on experience. I also understand completely how annoying it is when some newbie rolls in and starts rattling of yet another thread about how to make something awesome, fast, and cheaply. Meanwhile, you all are $20K+ deep in your shops and think that $700 for 100 bdft of quarter sawn white oak is an awesome deal! So it busts your balls to hear someone using the term Morris Chair, and 2 x 4 in the same sentence. I not only "get it," but I agree.
Here is the full story... I have a literal ache in my heart to build a Stickley Mission-style Spindle Bed. Gustav Stickley, and maybe even more so, William Morris, are literal heroes of mine. I have spent the past few years building mid-century modern coffee tables from Home Depot 3/4" plywood and veneering them with nice veneers that I get off the internet. But I have never built a full on, solid hardwood piece of Craftsman style furniture. I have been all over the internet looking for and asking for quotes on quarter sawn white oak so that I can make my bed. I have gotten pretty good at Google Sketchup, and have drawn up the plans based on Gregory Paolini's loose plan in this book. There are three large lumber yards here in Charleston, SC... and they all literally told me that they cannot do business with me on Quarter Sawn White Oak unless I buy 100 bd ft.
I am not broke, but I do not earn the kind of money that allows me to dedicate $1,000 to buying a pile of wood. So, I have to save and save for something like that. In the meantime, however, I want to go through the motions of building a Morris Chair, a Prarie Style Spindle Chair, and maybe a couple of bookcases out of el cheapo wood, so that I can see how non-plywood lumber works. And then along came my above-mentioned 2x4 project. So the light bulb went off. Maybe a better question would have been... what is a wood that I can afford that has the lowest price, but is still enough like oak to be of value to me as practice?