Does hair from beard for crown area look unnatural if it transplantation from scalp is already done before?

Scalp hair is usually the best donor hair for a normal hair transplant surgery.  You need to ask your doctor why the beard hair would be preferred over scalp hair.

         
It is preferable to do scalp to
scalp transplants in most people who have male patterned baldness, but if there
is a donor to recipient mismatch (or if scalp hair is too fine), beard to scalp
is the next best option. As long as the beard hair is nicely distributed in
between prior transplanted hair on the crown, it should blend well.

no , hair from beard that transplanted to crown area does not look unnatural . We do that often for donor site weak persons .. But growing quality is not the same as scalp hair. 

In general, the beard hair do grow well and slightly longer when transplanted in the scalp ( than the original beard area). They do mix up well but sometimes the beard hair may not come out that well also. therefore, the author always mixes the beard hair along with the scalp hair to get overall better results. It is also better to go for a smaller session of grafts from the scalp to avoid any over harvesting and thinning of the donor hair.

Beard hair can certainly be used as a filler in between scalp donor hairs in the mid scalp and crown areas. Scalp hair is always preferred but as a substitute beard hair can help add density and coverage as well as body hair. 

3500 grafts should be able to cover most scalp balding. I am not sure why you need another 2000 from the beard. Best to show your pictures