You are right, We can pick more keywords but we should pick only targeted niche keywords with supportive keywords like My domain niche Christmas quote then we can pick main keywords "Christmas quote" and pick also supportive keywords "Christmas song quote" "Christmas eve quote" "Christmas carols quote" "Christmas Halloween quote" etc..
Generally you can use 4-5 percent keywords in your over all text. You can use 2-3 keywords same time in the same text.
Each page of your website needs a main keyword. This should be found in the page URL, the title and within the 90 characters of the body text. After that use it 2% to 3% of the text. Extra, related keywords enhance the opportunity of being picked up by the search engines. The more related keys (both lateral and vertical) you can work into the text the easier it will be for the SE's and human visitors to understand what the topic of the page is. These are your long-tail keywords and the LSI for you web pages.
yes it has an limitation But i dont know exactly i have find this from an article few month ago.if you use more keywords then google or other SE can take you as spam so careful
Yes, every website have a limit of keywords. We can insert 5to7 percent keywords in content and 25 percent in their description.
yes there is a limit of keywords.keyword density shold not be greater than 4% if the density will be more then your site will not rank high in search