welcome to Goy

no I don't think you could class them as organic because of the use of the weedkiller.
check what the soil association says. they are the ones to ask.

Officially in the States, a farm has to be managed organically for at least 3 years before its produce can be certified as organic. Seriously overgrown land may require several applications of weed killer before manual control methods become practical, if you are short on labor, and, done properly, that can take a couple of years.
You may want to tackle the job in stages:
This year, manually clear a doable amount of land, digging out everything, and leveling and adding amendments as needed. Plant a cover crop suitable for your area, maybe peas and oats. Also try to brush out the rest of the land, removing as much woody material as you can. If possible, plant clumping varieties of native perennial grasses with a few wild annual legumes, to try to turn a field of weeds into a meadow, at least until you can get to it. If that is successful, you might want to leave strips of meadow on the land to encourage healthy populations of beneficial insects, and discourage the spread of pests and diseases.
Next spring, dig the cover crop in as early as possible, and manually remove any perennial weeds that you can find on the land that you cleared, then plant your first carefully selected crops, taking note of the quality of the soil. Clear some more land, and plant an appropriate cover crop for the summer, maybe buckwheat? Remember to dig it in before it goes to seed. Continue to brush out the rest of the land, as needed. Stubborn brush, such as bramble berries, may need the careful application of SBK to get a handle on them. Fine tune the meadow as needed, manually weeding and reseeding.
Then just keep on keeping on! :)

I think that you need to decide whether you are going to be strictly organic or just take on organic methods as can be practical. For example, you could, if the area is not too large, use a flame gun to kill off surface weeds and seeds rather than use Roundup or dig and hand weed. Only use organic fertilisers rather than inorganic ones. Would you want to buy organically-grown vegetable seeds rather than the usual ones. Even when importing manure from local stables you might find that the straw and animal feed that the animals have been bedded on or fed with might contain chemicals.

If the Veg are just for your own use then I do not see what is wrong with clearing the land using Roundup. As long as you are careful with the spraying so none of it goes on the soil, the chances of their being any residue in your food are minute. In theory the stuff becomes inactive when it is in the soil. Maybe true may not be, no-one is saying. Monsanto say it does, the organic freaks say it does not, but no independent body has come forward with properly conducted experimental data one way of the other.