Wassup! I haven't tried that particular strain from Seedism, but I do know Seedism has some great stuff. I used know the guy when I was living back in Holland. He's a good guy and loves his work.
As for the kushes, any of those would be nice. The RP OG #18 is always a favorite. Headband is a classic.. That'll for sure knock you out. The other ones I've neither grown nor tried, but just pick a few and see what you like best. Any of the plants can be finicky. Just observe the plants, check your levels(pH,E.C.) and your temps and humidity. Kushes are rugged plants and can withstand a lot.
For nutrients I would recommend Hy-Pro. They are new in America but very well known around the world. It's a Dutch company that's been around for over 20 years. They also created the original Amnesia, so you can guess that they're pretty good. I'm using it now on a whole grow.
Check my thread out. I just started it but you can see the results of Hy-Pro.
It's a simple 4 part nutrient package. Root stimulator, foliar feed(leaf spray), 2-5-5 plant food, and a pH- which also has a little bit of food in it as well.
Very simple to use. 5ml per liter on all products. Increase the amount of the Terra nutrient slowly through the bloom period. Has a nice feeding schedule on the bottle. I say give it a try.. Their slogan is "Quality and Simplicity"
They're many opinions about flushing. Some give at least 2 weeks, some don't flush at all. It's a personal preference. I like to flush 2 weeks before harvest. With a gradual decrease in nutrients in the last 4-3 weeks of flower. Some say adding sugar or molasses will help give a better taste. I've never tried it but it might work. I just stay safe and flush it will pure Reverse Osmosis water at a pH of around 5.7-5.8. The other flush products I think are a waste of time and money.
Hope that this has been helpful. Feel free to get back to me if you have any questions or anything. Enjoy your day!