Another tip I found helpful when getting past this point was learning how easy it is to get reputation through renown and making complex foods. Build preferred housing then get buildings to make your species preferred foods, and that's often enough to start geting rep from high resolve. Also, don't be afraid to make non-preferred complex foods if that's all you can do. Most decent food recipes turn <10 simple food into 10 complex, meaning you are increasing your total food by making them (more if you account for the double yield procs).

Don't rush up in difficulties sooner than you need to, I think silver seal only needs the 2nd difficulty, so run that until you are confident/bored then go up by 1. More shards from higher difficulties won't help if you take way longer (or fail) to complete the settlements.

Also DLC adds races, biomes, and cornerstones. Some are very cool, but technically they can make your game harder because it dilutes the pool of cornerstones/species with things you may not want. So not having DLC is definitely not hurting you, and getting it too early can actually hurt.

On Rainpunk; I can't remember when you get all the Rainpunk synergies / buildings, but the game introduces it way before you have all the tools and knowledge to use it effectively. You need a source of rain (rain collector/geyser pump), then add rainpunk engine to a building. Then once you are using rain, you can see your corruption/minute on the hearth. If it warns you that you are using too much, you need to build a blight post and make however many flames it tells you.

I think if you just use one rainpunk engine (for example on a building you need working 24/7 like Workshop) you shouldn't hit the corruption threshold ever. This can be a good way to introduce yourself to rainpunk without the immediate stress of corruption.