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I own a lot of EMDs and the keywords that they represent range from very easy to extremely difficult. EMDs will still rank extremely well if you have a nicely optimized website with a few pages that is in the google index and the level of competition is very low.  You don't need a lot of links, you just need to get it in the index.  Lots of people say that this does not work in google any more but I can tell you for a fact that it does.  I have #1 rankings with sites like this. This will work until some competition arrives.  When competition arrives the value of the EMD is tiny compared to the value of links and other assets.  Then you have to earn your rankings just like any other website. Should you use EMDs as a business model?  Probably not.  If you have a website of reasonable strength you can simply add a nicely optimized page to it and quickly rank above an EMD in a low-competition SERP.   I do it to EMD competitors all of the time.   I see lots of people coming into forums crying... "That spammer with an EMD is beating me  Wah!"   I chuckle at these because I have EMDs that get their asses kicked all of the time.   If an EMD is above you that webmaster has probably earned it unless there is no competition in your SERP and you have a website with zero strength.  Get off of your butt and get working.  You don't deserve to rank.  The EMD is a tiny advantage, if you are pissed off about it then just call the guy up and offer to buy it from him.   Then, a week after you take over the domain another weak site will move above you and you will be cryin' again.

with a "nofollow" attribute in the link code, yes, you can use it on the whole site. However, doing so can be seen as "tacky" / "less than truly professional".  That's why its suggested to be only on the home page footer.

I think in a way you are asking what is best from the SEO prospective... to use a logo as an image or to use it as a text? If this is the question that technically there is no problem either ways... if you are using it as text it will be counted as a text and if you are going to use it as an image you can always add alt tag to let Google know about its value in terms of text... But, from the user perspective it is better to have an image as it can give more attractiveness as compare to a text with CSS.