As the first major content release of Battle for Azeroth, patch 8.1: Tides of Vengeance is adding a number of new ways to gear up, as well as increasing the item level of rewards from existing activities. Tides of Vengeance goes live on December 11th and will add most of the new content, but Mythic+ and PvP Season 2 will not start until the new raid, Battle of Dazar'alor, releases in January, at which time the item level thresholds will increase to the new Titanforge cap of 425.
Fishing requires much time and does not yield much profit until its later levels. Unless you enjoy it for its own sake, avoid seriously delving into fishing until your level limit. It is not a bad idea to do a little when starting out a new character on a new server, though - the gray items you fish up sell for good money to a starter, which can help you out with your other tradeskills.
You could and it does make it even simpler (one button does it all) but I recommend against it. You would have to trust the undercut value. Because it also does a scan for the item when you alt click you can see that quite often there will be someone artificially lowering the item price in hopes to drop the price and buy it cheaper. Say some herb usually sells in stacks of 20 but the price for a single unit is 40g, which can go unnoticed (if no add-ons you'll only see the full price of the stack, not by unit) . Someone can easily pick one unit of that herb and post it at 20g or less.
If you're looking for simple, just get actionator. Set it to undercut everything you post for 1c and alt click from your bags. It will place the item on the ah window, do a scan for that item and autoset the price for how much you told to undercut (you can change it accordingly if you feel like it). It will remember if you do stacks for which items and replicate it everytime.