The other end is from pin 13 on the main plug..plain black and should have other end of white connector on it. If you cant find it the aerial amp just needs a 12v feed through black wire.
The cambelt on the is200 is easily do-able following the guide on here. I did one some time ago on one of my old 200;s and surprised me how easy it was.
Budget 3-4 hours and take it steady and double check everything.
http://www.lexusownersclub.co.uk/forum/tutorials/article/122-replacing-is200-timing-belt/
As Steve says; you cannot leave the Lexus range having owned one. Had Heather convinced about swapping our IS200 for something more comfortable.
Then realised she couldn;t bear me to sell it.....The alternative..get some softer full leather seats off a very kind member on here...^^^^^.
Once bitten....
The spark plugs look fine mixture wise. The threads on 4th from right look a bit iffy, so does electrode gap. The coils apart from 1 and 3 look quite new.
Regarding tightening, you have done what i always do, never had any problems.