Although Im sure you have already searched the boards for already existing threads

, here are some threads that bring up some useful points which might answer some of your questions:
Skink tactics
http://lustria-online.com/viewtopic...&sid=473b123e95a1ba88ebda222b29963473&start=0
http://lustria-online.com/viewtopic.php?f=15&t=204&sid=473b123e95a1ba88ebda222b29963473
Southlands lists & comments
http://lustria-online.com/viewtopic.php?f=9&t=153&sid=473b123e95a1ba88ebda222b29963473
http://lustria-online.com/viewtopic.php?f=8&t=34&sid=473b123e95a1ba88ebda222b29963473
That said, I have a couple suggestions for you as you build your list. First, as a primarily southlands player I must advice you that you can never rely on your skinks to win the day. No matter what, it is still going to be the Krox and Terries that will win you the game. The difference in a Southlands list is that the Skinks are going to be doing the gruntwork rather than Saurus. For that reason, always make sure that your list has filled the special and rare slots or you will often find that your skinks will not pick up the slack.
That said, for a list heavily featuring skinks and fast support troops, blowpipes are the worst armarment to have. Blowpipes are great for scouting units that can stay stationary for a turn or two, but for the most part your basic skinks will not be able to use them effectively. I would suggest a combination of 10% blowpipes (for scouts) 40% javelins and shields (for the units that are march blocking, baiting, and doing anything that involves regular movement) and 40% shortbows (the best weapon choice IMO, w/18" range these units can stay out of charge range of a unit while still being within short range at 9", these are the units that are going to do the 'swarming' by congregating around isolated units and shooting them up).
Skink units should always be between 10-13. You might want to boost a unit to 13 to avoid panic tests at 3 deaths, but any larger and your unit looses the manuverability that are its greatest assets. You want to be able to move units through openings between both friendly and enemy units while avoiding charge arcs, so the smaller the better.
When being charged, it really depends on the situation. With so many skirmishers and fast troops, it should be you dictating the circumstances of combat, not your opponent. You should position your Krox's and other combat units so that if an enemy charges your skinks, they will get flank charged in the next turn. For that reason, you should generally flee from a charge. This will normally result in a failed charge (guarenteed flank charge next turn), and will save you your skinks (assuming they rally). Standing and shooting is generally pointless as you normally will not cause more than 1-3 casualties. You should, however, stand and shoot if it is likely that your unit will be run down even if they flee. This way, you can take off a rank bonus if you are lucky.
Unfortunately, the rest of your questions are largely circumstantial depending upon your army list and the variables of any given game