I watched a tutorial on lynda.com about keyword research. And they said to use the All In Tittle trick to see how many pages on google are optimized for that keyword - do you reccommend using that method as well? In google, you type allintitle:"key word phrase" and the results show how many page titles are optimized for that phrase. Should I use this technique as well when choosing keywords?

I've done all of my keyword research, and now I'm selecting the KW's. In a previous question, seomoz had answered to pick a mix of easy, medium, and difficult words to rank for. How do I know which are easy, medium, difficult? The KW Difficulty Tool is not very specific. Is the level of difficulty related to where the phrase pops up for my company in search results? Are hard words ones that you do not already rank in the top 50 search results? When selecting KWs should I choose words that rank already in the top 50 that I'd like to try to move up? Or look for NEW phrases/words not in the top 50 results? Also, when entering KW phrases int the KW Difficulty Tool, Rank Tracker, and in Campaigns - do I need to use quotation marks if it is a phrase? I noticed that the KW difficulty tool has different results if you use quotation marks. Lastly, The person who did SEO before me has a list of KWs he optimized for, would it be valuable for me to include his words in my On-Page optimization efforts?