Let me answer your question about から (KARA) first.
1) からです （KARA DESU) and ですから （DESU KARA） are interchangeable.
If someone asks you "Why you are tired?", you can say;
A) あついからです。(ATSUI KARA DESU) = Because it is hot. Formal B) あついですから。（ATSUI DESU KARA) = Because it is hot. Formal C) あついから。 (ATSUI KARA) = Because it is hot. Informal
You can say either A or B in a formal situation. You can use C when you want to talk casually.
But when you connect the sentences ("the reason" and "the result") together, only the pattern B or C should be used.
B) あついですから、しんどいです。（ATSUI DESU KARA, SHINDOI DESU) = I am tired because it is hot. or C) あついから、しんどいです。（ATSUI KARA, SHINDOI DESU) = I am tired because it is hot.
They are grammatically correct, but please note that the sentence B sounds too polite and it sounds more natural to make the first part of the sentence (= あつい) informal as in the sentence C. But the sentence C is also polite because です is used in the second part of the sentence （= しんどいです）. As explained in Course 2 Lesson 10, the formality of the entire statement is decided by the verb in sentence 2 .
So if you just say あついから、しんどい。(ATSUI KARA SHINDOI), it sounds casual because there is no です at the end of the sentence.
2) Yuki sensei has answered a question about 〜けど (KEDO) before. Please take a look at this.