[asheshouse]

And i want to make a map 8)

That is all the reason you need --- Join the club.

It would still be interesting if you would post a map of the area you want to cover.

I think you can afford to go very large with this because the object density I think will be quite low.

--- but it is also possible to start with a smaller area and make it larger later.
If you do this it is probably better to prepare your microdem data for the large area and extract a section from it for your Phase 1 map.