@Simona:
Thank you for the photos - as they say a picture is worth a thousand words.
Let me say from the beginning that this is definitely
not my area of expertise - I am sure other forum members will be able to advise you.
Some observations though:
1) The hull certainly needs work - even with the damaged planks replaced she would leak like a sieve. An inspection inside the hull would perhaps provide a better guide on whether it should be completely replanked - see how well the planks are attached to the frames. If the planking is sound, perhaps it would serve as a base for fibreglass...?
2) The hull will need considerable strengthening particularly in the centre third to support the stresses of the keel, to support the mast foot and chain plates for the shrouds. Assuming it might be a Bermuda rig (mainsail and jib), you will also need strengthened areas for the backstay, forestay and jib pivot. You will also need to open at least one hatch through the deck for radio gear and servos. A boat this size requires a serious sail winch
3) There is no sign of a rudder or even a rudder post or pintle??? Boats of this shape usually have the rudder on the aft edge of the keel.
4) Keel - looks to be made of layers of timber? This will need to become a sizeable amount of lead (5 to 10 kg perhaps - no real idea)
To summarise - this is a big job. A very big job. At the end of the job, it may not be a particularly good boat to sail.
As a job, it would be much too big for me....
... but I am a very poor builder....
You could consider cutting your losses and finding another boat that is a bit closer to going sailing.???? In some respects, it would be easier to start from scratch and build a boat....
Hope this helps....