I would first check your axle and see if you have brake flanges.
I have put on electric brakes and hydraulic surge brakes and for your trailer I would go with the surge disk brakes. Here is a link and the cost.
This is a good unit and will cost less and work as well in my opinion.. lol'
If you have the flanges, and you probably do, you won't need a new axle.
I really like this much better than drum e brakes.
The first thing you may want to do, is weigh the trailer and then weigh the hitch. This will tell you exactly what you have. and as you add weight( bikes, gas, ect. you will have a better idea of where to put it and keep the tongue weight at 10% of total trailer and gear weight. When you first weigh the hitch it should be 10% of empty trailer.
I don't have E track on mine and use chain links welded to the frame for my tie downs. Then I marked where I wanted the rear tie downs and mounted thru the deck with steel backing plate.
Take your bike, and move it to where you want it(center of trailer and forward). Then move it to where you would place the next bike and mark for each tie down.
You may want to do this differently. Whatever works for you.
Put your lights where they won't get knocked off and use a good bracket.