Yes, 4-2-4 is correct. According to the sandhi rule of 一
i.e. 一 should be pronounced in the 2nd tone before the 4th tone.
And the sandhi rule of 不
i.e. 不 doesn't change the tone (the 4th tone) before the 1st/2nd/3rd tone.
BTW: 2-2-4 sounds weird to me.
No, this is not standard Pinyin, if this form of tone sandhi is written out. The author is simply trying to convey what it would look like if written out (instead of retranscribing it with Chao-style tone letters).
This type of sandhi ("Mandarin T2 Sandhi", for Tone 2 Sandhi), is mentioned only rarely, because it is a "prosodic-driven process", i.e. it ...
To the first question, I think 3rd tones are only full when its in the end of the sentences.
To the second question, I think it depends on how you do the segmentations. The last character in every parts will be 3rd tone while other are 2nd tones.
Let's say 米老鼠 would be segged as 米 / 老鼠, so the tones would be [3, 2, 3].
Some other examples: 剪指甲 would be ...