Which Range Extender should I buy (and other related home networking questions)

[1moreQuestion]

So here is my situation: I have the router set up in the basement in our townhouse, 1. because thats where one of the better lines is coming in with the internet (dont want to have to pay to rewire the house) and 2. because it allows me to hardwire to netflix to ensure the best connection.

The drawback is that it creates a spotty wifi connection on the other side of the house just one floor above, and basically no internet connection two floors up on the other side of the houes (causing my wife to eat up data with her cell phone because its not connected to wifi). To solve this problem I am looking to purchase a wifi range extender and have a few questions the i cant seem to find the answers to online. I am mostly considering the AC1200 model as I probably dont need the highest end, but even that may be more than I need, and I tell you this so you know where my mind is at.

1. Range. Are the ranges all the same? The specs seem to be mostly similar and its hard for me to determine what the actual differences are.

2. Speed. the AC1200 indicates 1200 Mbps, and the AC 1900 indicates 1900 Mbps speeds, but both of these are higher than our current internet speed (cant recall if its 25 or 50 Mbps), and I was not even aware that wifi speeds were that fast. What are the actual speeds I can expect with these range extenders?

3. Connection. is the connection seemless? in otherwords, if I walk upstairs, will my device pick up the strongest connection, or will I have to enter my device's settings in order to manually switch to the range extender everytime I move around in the house?

Lastly, I'm also planning on trying to wire ethernet to the top floor on the otherside of the house, this way we can have netflix up there as well. I guess my first question is whether I should run that cable into a second wireless router instead of just right into the smart device hooked up to the TV. This way I could have a wireless access point in a spot which is outside of my current wifi zone (I expect I cant currently put a repeater in this room because it would just be extending such a degraded signal that it would be worthless) and also have a hard wire access point with which to connect the TV for netflix.  (in which case, could you suggest a router/repeater/switch---its been a several years since I've been in this world so my terminology and understanding might be dated).

Sorry for all the detail, but I'm looking for answers for my first three numbered questions, but also feel free to let me know if I'm way off base.

Thanks for your expertise!

[TheEther]

1. The ranges are probably all different, though models with external antennas will probably have better range.  Unfortunately, no one can really tell you what kind of range you will see in your house.  It depends on so many factors: the construction of your house, the presence of nearby Wi-Fi  networks and other radio interference.
2. You definitely won't see 1900 Mbps out of an AC1900 class extender.  Why?  Several reasons:
1. AC1900 refers to the combined speed of the 2.4 GHz (600 Mbps) and 5 GHz (1300 Mbps) bands.  Most devices will generally use one band to connect to the extender. 
2. These speeds are physical link rates.  The actual data throughput is much, much less.  A good rule of thumb is to expect real world speeds to be no better than 50% of the physical link rate under optimal conditions.  Frequently, it will be much less.
3. There are very few devices that can connect at these link rates.  Forget about connecting at 600 Mbps on the 2.4 GHz band.  That requires non-standard Wi-Fi technology.  1300 Mbps on the 5 GHz band requires a device with 3x3 802.11ac Wi-Fi adapter.  Only Macbook Pros, high-end laptops and PCs with the appropriate Wi-Fi adapter can support it.
4. Extenders that operate in wireless, extender mode need to shuttle Wi-Fi traffic back and forth between devices and the main router.  This will further reduce speeds by 50%.  Many extenders can also operate in wired, Access Point mode where this penalty doesn't apply.  Not all extenders support Access Point mode (last time I checked, 3 Netgear models EX2700, WN2500RP and EX6120 don't support it).  Other than that, you would do well to run Ethernet to the top floor.  If you get an extender with multiple Ethernet ports, then it can service both wired and wireless clients.  You could also get an Ethernet switch to expand a single-port extender (i.e. connect Ethernet from basement, TV and extender to the switch).
3. Consumer grade Netgear products do not provide any assistance with roaming, so it will be entirely up to the device to decide when to switch to a stronger connection.  iPhones, for example, are prone to holding onto dear life to a connection, even when a stronger connection is available.  Some other brands have come out with better support (802.11r, 802.11k, 802.11v protocols for roaming).