If you just want to ignore crash recovery altogether, you can do that by turning off the fsync parameter. This makes the value for wal_sync_method irrelevant, because the server won't be doing any WAL sync calls anymore.
It is important to recognize that if you have any sort of server crash when fsync is disabled, it is likely your database will be corrupted and no longer start afterwards. Despite this being a terrible situation to be running a database under, the performance speedup of turning crash recovery off is so large that you might come across suggestions you disable fsync anyway. You should be equally hesitant to trust any other advice you receive from sources suggesting this, as it is an unambiguously dangerous setting to disable.
One reason this idea gained traction is that in earlier PostgreSQL versions, there was no way to reduce the number of fsync calls to a lower number—to trade-off some amount of reliability for performance. Starting 8.3, in most cases where people used to disable fsync it's a better idea to turn off synchronous_commit instead.
There is one case where fsync=off may still make sense: initial bulk loading. If you're inserting a very large amount of data into the database, and do not have hardware with a battery-backed write cache, you might discover this takes far too long to ever be practical. In this case, turning the parameter off during the load— where all data can easily be recreated if there is a crash causing corruption—may be the only way to get loading time below your target. Once your server is back up again, you should turn it right back on again.
Some systems will also turn off fsync on servers with redundant copies of the database— for example, slaves used for reporting purposes. These can always resynchronize against the master if their data gets corrupted.
max_prepared_transactions Parameter
Many people see this name and assume that as they use prepared statements, a common technique to avoid SQL injection, that they need to increase this value. This is not the case; the two are not related. A prepared transaction is one that uses PREPARE TRANSACTION for two-phase commit (2PC).
If you're not specifically using that command and 2PC, you can leave this value at its default. If you are using those features, only then will you likely need to increase it to match the number of connections