Customize the data that LTP is going to fetch with pre-filters like “Suggested Bid” (or Cost per Click [CPC], i.e. the amount of money an advertiser is willing to pay for a click on their AdWords ad that is targeting that specific keyword), “Local Search Volume” (average number of monthly searches for a specific keyword), “Advertiser Competition” (the amount of advertisers competing for a specific keyword) and “Number (of) Words” (very important when you’re trying to find long-tail keywords).
It's not always about getting visitors to your site, but about getting the right kind of visitors. The usefulness of this intelligence cannot be overstated; with keyword research you can predict shifts in demand, respond to changing market conditions, and produce the products, services, and content that web searchers are actively seeking. In the history of marketing, there has never been such a low barrier to entry in understanding the motivations of consumers in virtually any niche.
To answer your final question, yes but not really. You can definitely use AdWord keyword planner tool to get solid organic search volume estimates. However, don’t just stop there. Leverage other tools to find longer tail variations you can map against various stages of the buyer journey. I like to use SEMrush, Keyword Tool.io and Google autosuggest.
The limit on manual keywords could be higher. I personally wish we could input 10,000 keywords at a time, instead of 200. However, I understand the costs that Long Tail Pro has to maintain each time a new manual keyword is input. Not a deal breaker, I just wish the limit was higher. (To be fair, I don't think most keyword tools have a bulk manual option at all).