How many characters can you store in a binary(64)

Question

I have a procedure used to authenticate users in my db and it never crossed my mind to determine how long of an password a user could have in the db. I'm at the point where if someone wants to have a 100 char password, so be it, but I'm thinking I want to use this to account recovery questions as well.

Here is my procedure:

declare @PasswordHash nvarchar(100)
    = 'ThisIs101|ThisIs101|ThisIs101|ThisIs101|ThisIs101|ThisIs101|ThisIs101|ThisIs101|ThisIs101|ThisIs101|ThisIs101|ThisIs101|ThisIs101|ThisIs101|ThisIs101|'
DECLARE @salt UNIQUEIDENTIFIER = Newid();
declare @passwordHast binary(64) = (
                                       select Hashbytes('SHA2_512', @PasswordHash + Cast(@salt AS NVARCHAR(36)))
                                   );

if (@passwordHast = Hashbytes('SHA2_512', @PasswordHash + Cast(@salt AS NVARCHAR(36))))
begin
    select 1
end
else
begin
    select 0
end

Just to put it out there, in the use case for recovery passwords, there will be a system password not kept in the DB, however if there is a better way, i'm all ears.