Heroes of Might & Magic III: Horn of the Abyss

Can a bone golem be purchased in the Castle or only summoned?

A bone golem can be created from several skeletons.

And can 7 creatures still be recruited in each Castle?

No. Each Castle will have several additional creatures.

Are new composite artifacts planned?

Yes. At least 3.

Will there be changes to the old heroes' skills and specializations? Will the bonuses from skills and specializations change?

Specializations – possibly, but we are unlikely to change the skills. They are already quite good (in the options of WOG 3.58f).

And can I find links to the city websites? So far, I've only found the Dock.

The other cities don't have websites yet, but you can find information about Kronverk and the Cathedral here: http://www.woggrad.ru/
(The appearance of the Cathedral city screen will, of course, be completely different)