Dries, I think you're almost there but not quite - unless I'm misunderstanding what you have in mind.
You need a Bulgarian company to buy land - a Belgian one is still foreign so won't be able to own land. The formation of this company is really best done by a Bulgarian lawyer, just to be 100% sure there are no snags. There are some other people who offer a company formation service but I'd avoid them, especially if it's your first foray into the Bulgarian property market.
When you've found a property then the seller's lawyer will usually draw up the Notary Act and send it to your lawyer who will check it all, make any necessary amendments and return it to the seller's lawyer. Eventually, they will agree on the final version of the Act.
Try to avoid the preliminary contract - personally I always continue my search until the final Act is signed; problems can occur at any time and/or you may find an even better place at the last minute.
Ignoring the theory behind the preliminary contract, in practice it's only the buyer who's bound by it - being the only one who's put any actual money on the table. It just restricts your own freedom of action.
If you sign in person, remember that you'll need a translator; the contract will usually be in both Bulgarian and your preferred language (I'd stick to English if I were you unless you're happier with Dutch or French - whatever you choose be prepared to have a smile at the way it's phrased!). However, it's only the Bulgarian version which counts and if there is a difference in the non-Bulgarian one that's too bad. The notary will insist that a (usually) qualified translator does a simultaneous translation for you as he/she reads out the Act aloud. Depending on where the signing takes place, it's best to have your lawyer present to check the Act on the day, just in case there have been any unauthorised changes made.
Payment should be made by bank transfer, so there is a "paper trail" and you need to make arrangements for this beforehand, otherwise you could end up arguing about whether you're happy to transfer the money before the seller signs, or they're happy signing before the transfer has gone through.
The best approach, in my experience, is for buyer and seller to open accounts in the same banch of the same bank (in leva, euros or pounds - all very quick and easy to do). Everyone can then sign and leave the papers with the notary. The buyer & seller then go to the bank together to do the transfer and confirm it's in the seller's account. They then return to the notary, who releases the papers once they've seen the printed confirmation from the bank; usually this will be appended to the Notary Act. It's a bit of a long-winded way to do it but I prefer it as everyone's covered.
Don't forget to ensure that all bills have been paid before you sign and remember you have 30 days (I think) to register the change of ownership at the municipality offices - you'll get a fine if you're late! You'll need a certified copy of the Act to do this and while you're doing it, you might as well get the water, electricity (and gas if it's connected) done at the same time since they'll ALL need to see the Act.
If you're going to leave the property unoccupied, or even if you're not, don't forget to organise insurance. Unoccupied properties can be attractive targets for burglars and you don't want to find holes in the walls and ceilings where your pipes/cables/kitchen unit/sanitary fittings etc used to be with no insurance to replace them.
