个 is a measure word. It must be used if you are describing how many of something there is. There are many many measure words in Chinese, but usually 个 can be used in place of all of them. Obviously if you know more, you sound more native. English does have some equivalents. If you are talking about "tape" (like duct tape) you don't say "I need a tape". You say "I need a ROLL OF tape". "Roll" here is the measure word. For example, you would say "一个“ to mean "a" or literally "one of" something. You just need to get used to putting 个 between a number and a noun.

I have found this website which searches for words and phrases and their frequency. Very useful! http://www.wordandphrase.info/frequencyList.asp It will show you the rank of the word in common publications, as well as the category of where the word is found. Try it out! For example, "concomitantly" is ranked at 30000th or so, and is used primarily in academic publications. "Denim" is ranked 10000th and found more in fiction and magazines. I can say from everyday speech, "denim" is much more frequent then "concomitantly". The website would agree as "denim" is found in more common publications (magazines) and "concomitantly" is limited to academic papers.

"Are you having as much fun as we are?" Yes! This is exactly right. You may see "Are you having as much fun as us?" but "us" is wrong here. "I don't have a good history in love. / I don't have a good track in love." Close. "I don't have a good history WITH love" or "I don't have a good track RECORD WITH love" "I've realized how much I love you." Perfect "I'm sorry the way I spoke to you." This is mostly good. I would say "I'm sorry ABOUT the way I spoke to you."