Sticks and stones side-quest

[River's]

Hi guys,
I am doing a first almost blind playthrough and I would like to receive as spoiler-free as possible answers to the following questions regarding the Sticks & Stones sidequest that I have just started:

1- if I talk to Blackroot after I have 3+ stones, can I choose not to spend them immediately in case I do not like the upgrade he offers (if he explicitly states the upgrade... I dunno if he does)?

2- are any of the stones missable in one playthrough?

3- if I have a combination of stones that I want to trade, should I just trade it with Blackroot as soon as possible or is there any reason to keep them until late-game?

Thank you very much.

[masaki]

A1 You can
A2 A lot,better following this collection guide[www.gamesradar.com]
A3 If you only want to finish your first walkthrough not to start new game+,you should trade it with Blackroot as soon as possible(when you consider about what kind of way you wanna play)

[darth.crevette]

There are NO missable anything in the game. You'll never be locked out of any area at any point in the game, so you can always go back to get a stone, relic, page, etc you missed.
The only exception is the one chest in the tutorial area at the very beginning (that only contains 3 health potions).

[River's]

Thank you for your answers. Glad to know there are no missable items.