Everyone is affected differently, so I'd really recommend trying each thing on its own first if you have the patience. You don't know if you're going to get some weird reaction or something if you've never tried any of them before, so it's nice to take them one at a time first. If you don't like something at least you'll know which one it is. If you're combining some of these you might to use lower doses, since they will synergize with/potentiate each other and you've never taken any of them before. The skullcap, siberian motherwort, and wild lettuce all sedatives, while the kanna and kratom can both be stimulating and/or sedating. I think I'd at least use the kratom by itself.
Dosages are hard to say, it will depend on whether you're eating them, smoking them, or making a tea, and on the quality of the plants you have, and of course everyone is so different. You could always start low and increase. The dosages below are just what a lot of people like/recommend for an oral dose when taken by itself, they are by no means exact.
kanna - initially stimulation, often followed by sedation; elevating yet calming
avg starting dose: around 500 mg
skullcap - mild sedative, calming, relaxing (believed to be similar to a benzo in action)
avg starting dose: around 1 g
siberian motherwort - mild sedative, said to give a mild cannabis-like buzz; often used in herbal smoking blends or as potentiator for cannabis; looks like cannabis
avg starting dose: around 500 mg - 1 g (some sites say do not take more than 3 g in 24 hrs)
wild lettuce - mild sedative; calming; some people are allergic; many find it disappointingly mild (I guess they are expecting it to be like opium); some say a tea is better than smoking; overdose can apparently be serious
dosage: I have no idea, I haven't tried it and dosages others use are all over the map, plus depend on the ROA. A few sites say to make a tea with 1 tsp.
kratom 15x - both stimulating and sedating, depending on the type; an opioid; too much can be unpleasant
avg starting dose: hard to say as they vary a lot, maybe around 1 g?
ETA: I forgot you also asked about methods of preparation. Any of these could be made into a tea. To improve the taste you could add some lemon, honey and maybe some calming herb tea like chamomile or something.