It is probably safe to drop them all at once.
In general, deleting a table is very fast, regardless of the size of the table. DROP really does not modify any data, Oracle just changes the data dictionary to mark the space as available. I have lost many tables with hundreds of gigabytes or more of data and have never experienced a problem. (Your data files can no longer be sorted, but this is another problem.)
With the exception of dependencies and locks, the only time I saw a crash was (relatively) a long time due to the delay in clearing the block. Basically, if you update, delete, or insert (without adding) a lot of data, Oracle can write some transaction data in blocks. The reason for this is to make COMMIT instant, but this means that the next query, which even reads from the table, can clear old transaction records.
But your chances to face this problem are small. If you have very large tables, they were probably created with direct path inserts, or someone else already requested the table and cleared the blocks. Even in the worst case scenario, if your system was good enough to write data, it will probably be good enough to get rid of it (although you can run the ORA-01555 snapshot too slow if the transactions are too old or from the archive the log space from additional repeat from deferred block cleaning, etc.).