For what it's worth, I think there are very few jobs where you actually NEED a ratcheting wrench. Sure, there are some jobs where it's a right pain to keep locating and removing a conventional wrench, and the ratcheting ones are great, but that's in the 'nice to have' category rather than 'need'!
A good set of socket wrenches and accessories is different though, you do need these! How so? Well, half a century ago, a designer would design most machines or vehicles so that they could be taken apart using regular wrenches. Books like 'Machinerys Handbook' set out how stuff like how to space bolts so that an open end wrench can always turn them!
Not so today. Designers cram stuff into engine bays and quite often the ONLY way to get at a fastener is with a socket on a long extension. Even things like Torx screws and Hex screws can often not be removed with a torx screwdriver or hex key. So, ensure you have a comprehensive set of sockets, plenty to turn them with (Maybe a flex head ratchet if you don't own one) and, depending on your vehicle, a set of hex bits or torx bits as well, before the ratcheting wrenches!
Good on you for tackling the head gasket! As you do more jobs, you will often find a need for something you hadn't though about. That's the time to buy. You might want to think about stuff such as a Torque Wrench too!
Beware though, once you start acquiring, you'll only want to stop when you own EVERYTHING!