Generally, I tend to think if someone is doing light touring, that someone is either camping with a minimal level of comfort (roughing it out) or with a credit card and hotel/motel options. Also, most of the penalized weight you bring on tour are going to be realized when there are a lot of hills to climb. If you're fighting against headwinds, and you do if you tour along the coast, aerodynamics is your concern. Of course, with panniers sticking out like a pair of sails and your more upright riding, you have to be realistic how much you want to tour light weight vs the benefits and the comfort you gain or lost by being a weight weeny!

My advise to you is simple. Use your early weekend or 2-3 day tours to build experience. It's fine to be slightly overloaded during your beginning tours. Almost every expert tourer I have known thus far had, in one way or another, been overloaded. Bring as much as you feel that you will enjoy on the tour with and then on your next tour, re-evaluate what you can bring without or be without.

In terms of repair supplies. You should bring only tools you know how to use to repair your bike with. I have met so many newbies out there who have every single repair tool (chain tool, spoke wrench, spanner, etc plus a flat repairing kit and a repair book) they brought along only to expect to repair like a bike mechanic expert by reading a book on the spot!! Know how to change a flat or fix flat. Know how to change a spoke and then true the wheel in the field. If you don't know how to fix your bike, then all those tools you bring are simply dead weight. So before you plan on going on a longer tour, try your hands by servicing your own bike rather than rely on a shop to do this for you. The more you are familiar with the bike, the more you can be self-sufficient.

Lastly, the lighter you want to go touring wise, more comfort will be sacrificed. Some people can be in the least comfortable, but tour light. I once met a french guy who toured worldwide just with a fur coat and a garbage bag. Seemed like a happy guy and seemed to do just fine. I pale in comparison with 2 small panniers and 2 medium panniers with all my camping, tools and stuff during my 8000 miles trip against his just 1 garbage bag.

While this site is aimed more at off road riding, there is good info for lite-weight " bikepacking " here. https://www.bikepacking.net/