I would suggest the "keep it simple" approach ....
- Buy a pair of hi/lo beam H4 inserts (most also have a parking globe holder, if you need it)
http://www.ebay.com.au/itm/HEADLIGHT-IN ... 45f9ff9700
- Buy a pair of H1 high beam inserts
http://www.ebay.com.au/itm/HEADLIGHT-IN ... 3ef0b2490f
Note : Hella or Cibie inserts are much better, but also cost heaps more. I have found these ones fine, and if you break one it doesn't hurt the wallet too much !
- throw away the globes that come with them (or keep them as spares) and buy some
good quality globes. Any of the European brands like Phillips, Osram, Hella are good ... Narva are also OK ... but don't go anywhere near the cheap ones they stock at SuperCrap and the like. (Personally, I use Phillips "Crystal Vision" globes). Go 100w/90w H4 for the outers, 100w H1 for the inners. Don't bother with anything higher wattage than that ... the globes don't last.
- use good quality relays, and good thick wire between relays & lights (also the earths) and from battery to relays. Make sure you have at least 13v (not 12v !) at the back of the light .. check with a multimeter. Halogen globes are designed to put out their rated wattage at 13.8v, not 12v, and at 12v they are only around 80% efficient and it gets worse from there ....
- get your lights properly aimed ! Many workshops have headlight aligner boards, and the small amount you will pay to get them aimed accurately is well worth it compared to DIY ... the difference is very noticeable.
A setup like this will be more than adequate for road use.
As far as wiring it up etc goes, this website has lots of useful info ...
http://www.rallylights.com/FAQ.aspx
Just as an aside, the eBay seller shown above seems to stock a few different rectangular H4 inserts ... he might even have some to suit a GA ? I have bought a bit of stuff from him over the years & found his service to be good.