Hi Watty,
Congratulations on your recent acquisition. Sounds like this is your first foray into the wonderful world of land sailing.
It would help to know if your blokart is brand new or second hand.
I assume your down haul is the standard (non adjustable while underway) set up.
Generally speaking more wind more downhaul.
Sooner or later your pulley whip will snap off at the socket. When this happens take the broken bit out of the socket and put it in your pocket making sure you do not lose the metal clip. Shove the whip back into the socket and continue sailing.
When you get back to the car or home you will have to trim the broken end square and drill a hole for the clip. Doing this you will lose about 50 mm of length. The pulley whip is good for about 4 or 5 breaks before you will need to replace it.
In the competition rules there is a minimum length for the pulley whip. A shorter whip gives you more sheeting scope which may or may not give you a little more speed, depending on conditions. When it becomes very short you reach a point of diminished return.
The addition of the mast crane is a good idea as it positively sets the sail height on the mast eliminating the stretch inherent with the turban set up. I doubt it has any effect on performance or better tacking.
Probably the best thing to do for better tacking is to spray your mast with some pure silicon.
The addition of the adjustable downhaul kit is not a bad idea but is more of a convenience than a performance enhancer. When you are going really fast you will usually be too busy to be mucking around with it.
The thing to keep in mind if you intend doing any racing is that almost any mod will put you in performance class rather than production class.
Last year at the Nationals at Yeppoon, my standard production class blokart, in the hands of someone who knew how to sail (not me)
beat the pants off the performance class blokarts.
I see you are located at Rosewood which is a fair way from any beaches but there are no doubt some open flat areas and maybe airstrips around Lowood where you could have some fun. Please feel free to post pics of your favourite locations and if you know how (I don't)
post Google Earth reference links to them.
Below are some links to other blokart sites and forums.
www.blokart.com.au/forum/ http://www.blokart.com/#MapFramez3.invisionfree.com/CQBC_Forum/index.php?act=sitebbkc.freeforums.org/new-aus-blokart-forum-t23.html
and 
