Morch,
(1)It seems to me that often after the 3rd line is in place it's confirmation that a retracement is more likley?
Sort of. There is nothing magic about the number 3, but the steeper the uptrend, the less sustainable it is and the bigger the retracements tend to be. All uptrends have retracements though - they are an integral part of any trend.

(2)Is the longer trendline of the three the most likley one to indicate future support?
It's not the length of a trendline that indicates its reliability, so much as the number of times it has been "respected", ie the more points of contact, the greater the reliability and the greater the significance of any subsequent trendline break.
This might seem like splitting hairs, but to me, trendlines do not "indicate future support". They are there to show me when/if the uptrend weakens. In other words, I use them to monitor an ongoing uptrend, rather than in an attempt to predict future price action.

(3) Do you always draw your lines using the closing price? and if so why? I often use OHLC
It is commonly accepted that the Close is the most important of the OHLC prices. Generally the Open is assumed to be controlled by the amateurs who have entered their buy/sell orders outside market hours, and the Close is assumed to be dominated by the professionals who are acting as a result of that days price action.
In any event, all my medium/long-term systems are based on Closing prices, so I make most of my buys and sells near the end of the trading day. My shorter-term systems utilise all 4 prices, and to depict them, I use Candlesticks almost exclusively.