Well, not to say that I'm the one "who knows a lot" about solar, but hopefully enough to answer some.
1) I am just wondering if this is a good relatively cheap way to get started with solar? Yes. $125 for 140W panel with free S/H is a good price even if it were a panel alone. Consider that you're buying just a panel. Amazon has never been a good source for panels or controllers. Description like "... blocking diode and a bypass" is funny. What "bypass"? Like a highway around big city :)? I would guess that our not-so-learned Chinese friends meant "bypass diode", but then the question is - how many?
Let people who really know "a lot" about solar, analyze this cryptic text and make educated guesses. I prefer buying good panels from reputable brands. With known number of diodes and good frame. There exist good Chinese domestic brands, if you're on a budget.
2) Is it ok to have 3 or 4 separate controllers?No. Besides, what you're getting here is a cr-ap of controller, so getting 4 of them will 4 times increase the chances that system will cr-ap out when you expect this the least. If you buy 3 of those, throw controllers out and get a single 30A controller of PWM type. If you buy 4 - then get 40 or 45A controller. The wiring is easier with one controller, this is reason big enough for me.
3) This looks like a pretty good price to get started and figure I could mount 3 of these on my roof and have a decent amount of solar to get started?Yes, good price for 140W panel. If you get 3 - then get a proper 30A controller.
Consider the panel size. Make a template of that size and see if 3 of them fit on the roof and there is at least 8"-10" to air conditioner and/or vent lid, so they won't shade the panels.
Here is a popular source for panels:
Solarblvd. Their 140W panels are square, 3*3 ft, this may or may not work better than those panels from Amazon.
Don't want to pour too much info onto your head at once, but with 420W roof-mounted solar array people usually go for 2*200 or 2*250W panels. Those are roughly 3*5 ft and weigh 40 lbs each, no matter if it's 200 or 250W, same size and same weight. The biggest difference from your planned panels is that they have a higher nominal voltage - 24V - so they require a different type of controller, it's called MPPT and costs more than PWM.
With 420W array made of 24V panels I would buy Rogue 3048 controller. There are cheaper 30A MPPT, but there isn't anything better. Not to say that you HAVE to have 420W made of 24V panels and MPPT. You may as well have 420W made of 3* 12V panels like the one from Amazon, and PWM controller.
