You will have to re-query in order to get the Autonumber because the autonumber is not created until the data has been inserted (or appended).

You should consider creating a function that will query the table to get the last ID number used and then increment it. THen you will know what the ID number is before you insert it. One additional item to note after you change the column from an auto number into a number field type make sure you change the index so that duplicat numbers are not allowed, so that a duplicate ID number is not entered.