You are totally right, I swear me and other members have answered the exact same questions before. Just searched for about 10 minutes for the old posts, and never found them, Hahaha.
Anyways, kara FB motion is qcf MK~lp/mp/hp ( You basically Kara cancel, aka P-link, Mk with a punch button ). It’s also the same for kara srk, just the regular SRK motion, and plink mk with a punch.
St.lp > U2 is a legit link, no counterhit required. It’s a one frame link, but remember you can plink the KKK button with HP if you like, but don’t worry about that. I found that most people don’t see it practical because of the motion. You don’t have to do it too fast, just be on point, it needs practice. I personally think of it like this: cr.lk > cr.lp> st.lp qcf > qcf KKK. I know this might not make any sense to you, but it helped me alot with this combo.
Most damage and stun is st.hk > ex tatsu. Ex SRK leaves you at a very bad position, you can’t do a safe fake thunder kick afterward, but you can go for a true thunder kick, but they can still wake up with a shoryuken or something. Still, I prefer heavy SRK over EX srk as a combo ender.
Here are some post-ex.tatsu mixups. Cr.lk on first frame > cr.lp+cr.hk OS> combo, this will stuff their grabs and any normal they attmept, since you are at +1 frame advantage after the ex tatsu, backdash gets blown up by the OS sweep ( You can look in joon’s thread to see which option select works on who: http://shoryuken.com/f259/ssf4-ae-ken-improvement-thread-210528/ ). You can also go for late cr.tech, if they grab you tech it, if they DP you block it, if they backdash then your late cr.tech ( aka cr.lk ) stuffs some of the character’s backdashes ( ryu/ken/viper comes to my mind ). You can DP straight after the ex tatsu for chip damage or if you expect them to dp, your mp.dp beats most of the dps in the game ( except ryu’s ex ).
In general, I see most ken’s go with U1 in tourneys. I personally use U2 as my default ultra, and U1 for specific characters or for online matches, Lol. Keep in mind that U2 can be combo’ed from an FADC combo too, which is cr.mk>hadoken FADC U2. U2 has more combo-ability but it depends if you can land it or not. U1 is still the most damaging though. I use U1 for Rufus, Blanka, Chun-li and E.honda.