It depends on the composition of the field as it currently is. If it is mostly grasses and weeds, then religious cutting every week, and fertilization at the proper rate/type, and overseeding will work out good. You can get a soil test kit from your county extension agent.. or at most farm supply feed stores. Some tests have to be sent in.. but others are home testers using water/activator liquids. Not exact on the home testers.. but gives you an idea to shoot for.
Religous cutting is great for the grass.. and hard on the weeds.. especially things like briars that rely heavilly on good timeing to dispurse their seeds.
Cactus is another story. If there are isolated patches.. you will do just as well to go dig them up and dispose of them.
I did my 13 acres like that.. and have -0- cactus now.. only took 3 weekends with me and the wife.
We used 33 gallon trash cans and a 4 tined hoe and a spade shovel. The 4 tined hoe pulled the cactus great leaving the dirt. The shovel was for the occasional deep root, or large patch. We already had a burn pit and just hauled can after can of cactus over there. Watch out... the smallest pieces you leave can sprout. I also don't reccomend actually trying to pick any of the cactus up by hand.. even with leater gloves... Early on we tried this and found the small w\little wiskers work right through the leather gloves with no problems... let the shovel and hoe do the work.
Now if ya got lots of cactus... just disc and disc and disc till you can't disc no more ( popeye's motto .. I canst' takes no more.. ).. and that should do ya.
If it is heavy brush / briars I reccomend you cut it, then disc it if there isn't alot of thatch.. or if there is.. you may even have to plow it under first.. then disc it. Depending on the plants, you may have to disc it again. Try to time your work up with the plants growing cycles.. your extension agent will be able to tell you when undesireable plants are at their most vulenerable point.. like when saving food for root storage for winter.. etc.
Seed and fertalize the soft bed, and drag with a light flexible harrow, or old mattress box spring... or an old piece of fencing with some blocks or railroad tie laying on it.
good luck
Soundguy