Grammar notes 46

Another way to express obligation is with the て form of ーない, ーなくては(いけ|なら)ない.

と may be used at the end of a sentence to produce a differential, akin to when/if.

ーないで is used when the following sentence is a subordinate to the previous statement, but not an underlying cause. On the other hand ーなくて implies there is a reason, so that first statement is the reason of the following statement.

なくはない is a phrase, as such any closer look would be redundant, it would be equivalent to "you could that that, but you could also do this".

Grammar notes 45

ーたら is another conditional. It it creating by for yodan
Replacing ending with
る　->　ったら
く　->　いたら
う　->　ったら
す　->　したら
つ　->　ったら
む　->　んだら

For itidan replace the final kana with たら.

としたら　or とすれば or とすると is another conditional, the condition being stressed. It used used in the pattern Nとしたら where N is a verb in base 3.

ーたら　vs ーえば is according to the textbook hard to explain. I concur.
ーたら is more oriented with timing, while ーえば may be seen more as a prerequisite for the following statement.

Grammar notes 44

If can be expressed in two ways. One of them is to vowelshift the last character to え and appending ば, ーえば form. The implication of this form is that if A happens B will happen as a natural consequence of A. AえばB.

A second way to express if is by the word なら/ならば.

The pattern ーえばいい(良い) could be consider the english equivalent to "You should".

The pattern "the more/the less" is tricky. But basically it's
AーえばするほどB
The more of A, the more of B.

ーなければなりません is used to express obligation to do things, although ーなければいけません when you are obliging others.