For (a), text search *can* do that. That's pretty much what we use on AskTOM here to provide search.

We want an index across "all" the text columns that make up a question, an answer and the reviews. So we have a procedure to do that:

CREATE OR REPLACE PROCEDURE  asktom.ate_question_idx
(rid in rowid, tlob in out nocopy clob)
is
begin
for c1 in (select q.subject, q.question, q.answer, q.id
             from ate_submitted_questions q,
                  ate_admins a
            where q.rowid = rid
            and   q.admin_id = a.id(+)
            )
loop
    tlob := tlob || c1.subject || ' ';

    if c1.email is not null then
        tlob := tlob || c1.email || ' ';
    end if;

    tlob := tlob || c1.question || ' ';

    if c1.answer is not null and length(c1.answer) > 0
    then
        tlob := tlob || c1.answer || ' ';
    end if;

    for c2 in (select review_comments, followup_comments
               from ate_question_reviews
               where question_id = c1.id
               order by created_on)
    loop
        if c2.review_comments is not null
        then
            tlob := tlob || c2.review_comments ||' ';
        end if;

        if c2.followup_comments is not null
        then
            tlob := tlob || c2.followup_comments ||' ';
        end if;
    end loop;
  end if;

end loop;
end;

and then we can define a text index that uses that output at the "column" for the text index to be based on

begin
  ctxsys.ctx_ddl.create_preference('ATE_SEARCH_IDX_DST','USER_DATASTORE');
  ctxsys.ctx_ddl.set_attribute('ATE_SEARCH_IDX_DST','PROCEDURE','ASKTOM.ATE_QUESTION_IDX');
end;
/

create index ATE_SEARCH_IDX 
  on ATE_SUBMITTED_QUESTIONS(ANSWER)
  indextype is ctxsys.context
  parameters('
    datastore       ATE_SEARCH_IDX_DST
    sync (every SYSDATE + 4/24 memory 67108864)
  ')
/

So even though the index is defined for on the "ANSWER" column, the procedure above means that we'll go collect all the other information as well to put in the index.

For (b) ... no we don't do the "auto correct" but we do provide fuzzy search capability

https://docs.oracle.com/database/121/CCAPP/GUID-098F287A-DD02-42E1-B685-B1E4ED108FBA.htm