Hello,

this is my first question in the forum, so forgive me in advance if this is a trivial matter, wrong sector, already asked question etc.

Earlier this year i bought the wiki extender powerline, a base + device, TL-PA4010 and TL-WPA4220_AV600 (is this called the PA4010 kit?).

Since i found it incredibly useful, I have some very easy questions:

how many other extenders can I add? Can I buy more of those, without buying again the base device?
Do too many of those influence negatively the efficiency of the internet connection?

And most importantly, which ones are compatible with the base that I have? 
Thank you in advance for any of my questions you'll want to answer.