Can someone please explain to me the differences between the following interrogative type words?
いくらか/いくつか
いくらも/いくつも
いくらでも/いくつでも
いくら/いくつ/どのくらい (in questions)
For example I know that いくらか and いくつか both seem to mean "some..." or "several..." but are they used in slightly different situations or are they interchangeable? etc. etc.
I doubt いくらか/いくつか, いくらも/いくつも いくらでも/いくつでも should be called "interrogatives." They don't make a interrogative sentence by themselves. いくらか = "some (uncountable)", いくつか = "a few (countable)", いくらでも "no matter how many/much (countable/uncountable)", いくつでも "no matter how many (countable)"
いくらも is slightly uncommon. I think it's mostly used together with ない especially in literature, as in
いくらも残ってない
[we] don't have much left
On the other hand いくつも is very common, = "a lot of"
いくら is an interrogative. It can either mean "how many" or "how much is the price", but I think it increasingly means only the latter nowadays.
このサバいくら？
How much is this [slice of] mackerel?
On the other hand いくつ and Chinese-originated 何個(nanko) is taking the place as an interrogative for number of items.
いくつ/何個 必要ですか？
How many do you need?
The notable usage of いくつ (not 何個) is asking the age of a person:
失礼ですが、お幾つですか？
Forgive my rudeness [if you don't mind me asking], how old are you?
どのくらい is also an interrogative to ask "to what extent" "to what degree" or "how intense." It's very versatile.
このお肉、どのくらい焼けばいいですか？
How long should I grill this piece of meat?あれからもうどのくらい経っただろうか
How much time has passed since then
It can even mean "how much":
この壁にはどのくらいのペンキがいるかな？
How much of paint do we need for [covering] the wall?
"いくら" means "how much", while "いくつ" means "how many". This is the main difference between the two words. "どのくらい" means "(about) how much" and is very close in meaning to "いくら".
The "か" particle on "いくら" and "いくつ" give them both the meaning "some". This, of course carries the meaning of some specific number of discrete things, for "いくつか" and a more analog amount for "いくらか".
From goo辞書
いくら‐か【幾らか】
1［名］あまり多くない数量。いくぶんか。少し。「収入の―を貯金する」
2［副］数量・程度があまり多くないさま。多少。「きのうより―気分がよくなった」
The "も" particle on "いくら" and "いくつ" give them the meaning of "a lot".
From goo辞書
いくら‐も【幾らも】
［副］
１ 相当多い程度。たくさん。「そんな話なら―ある」
２ （打消しの語を伴って）それほど多くない程度。ほとんど。「在庫はもう―ない」
Appending "でも" gives the meaning "no matter how much", "a lot" or "plenty".
From goo辞書
いくらでも【幾らでも】
1 〔制限なく〕
⇒ as much as [he] likes
2 〔わずかでも〕
⇒ no matter how small
