Secret
Alucard painting, room, and outfit
Portraits, then the tower
The Main Hall has more than one portrait of Alucard. The Alucard Guides clue sits in the Old Gallery and is filed under The Artist. Alucard's Tower is past the Bridge of Knowledge, in the upper castle, behind blue flames you have to clear. Inside are a letter from Adrian, a portrait of Lisa with the infant Alucard, and a shrine.
The tower reward is Alucard's Sword and Shield, a legendary fourth-tier weapon and shield. Reports of its attack value disagree across wikis, so this page does not print an attack number. The moves that are described without a number: the attack can blink, and holding the button raises the shield. Alucard himself is not confirmed as a playable character, a boss, or a story appearance.
The outfit is not in the tower
The Alucard Style Costume is a preorder and early-purchase reward. Konami says the physical edition has to download it separately. It is not the chest at the top of the tower. Portuguese searches for the outfit and for the room are both this page, in two sections, so neither gets the other's reward.
What I ran into
I climbed the tower looking for the coat. The chest was a weapon. The coat was on the store page the whole time. Those two facts are now in different headings so I cannot merge them again by accident.
Questions
Where is Alucard's room?
Alucard's Tower, upper castle, after the Bridge of Knowledge, behind blue flames.
Where is the Alucard costume?
It is the preorder bonus, not a tower drop. Physical copies download it separately.