To be legal does a lease over one year have to be registered at the land department?

No, only leases over 3 years.

Can you lease a property from day#1, as just arrived or do you need to set some paperwork first with the local authorities in order to be able to do so ?

You should have no problem. Landlord should register you as an alien living at there property.

Landlord should register you as an alien living at there property.

I wonder how many actually do this? Very few, I suspect, when it comes to condos.

Of course the business of being registered with immigration has nothing to do with the legality of a lease, nor with the possibility of taking one out. The person who owns a property in which an alien is staying should report it anyway, regardless of whether a lease is signed or whether any payment is being made. Again, I dont suppose that many do, apart from hotels.