1) 船長は皆に宝を残してくれた。さあ、遠慮なく使うがいい!
What is the meaning of this ~がいい? I read the explanation here がいいの類語・シソーラス - 類語辞書 - goo辞書 ([2]), but it doesn't feel like either of these 放任・非難・軽蔑 because it has さあ before it.
I think he is saying さあ、遠慮なく使え! while also saying "using it is the best choice".
2) The next questions are from that explanation of ~がいい.
ところが、「がいい」は自分自身のことには使えず、相手に対しても提案というより、どうとでも勝手にしろといった放任・非難・軽蔑(けいべつ)などの気持ちをぶつけることになり、使用範囲が限られてくる。
a) In 相手に対しても, is も "also/too"? ("Towards 相手 as well/too...")
b) What does ~てくる in 使用範囲が限られてくる show? I think it indicates the direction of the action ("towards us" OR "to us").
Thank you! I think I understand the meaning, but I can't tell if this meaning is derived from one I already know or not. Does any of the following meanings fit or should I consider this a new meaning?
Ahh, I see. Thank you! That's the one I was thinking about when I asked if it is like 雨が降ってきた, but I see now that the definition covers more than just one meaning.