1) Are they viable to use at frosties?
2) Are there occasions where I'd still be using spec restores?
3) I do intend to get back to slayer. At least 93 slay or higher, to max melee and get yak. Would there be tasks that I use spec restores?
4) If not 2k, what would be a more appropriate amount for me based on the above situations?
Thanks for the advices!
The very best way to get high herblore is to just make your most efficient pots (use the Grimy sheets to determine this) until you can make spec rests and super antifires. Then make around 1k super antifires for slayer and 2k or so spec rests, then I would make 1k of each extreme with 2k of extreme attack and strength. This should put you around where you need to be to stew to overloads (91+ herblore), then you just make overloads as you need them.
This will give you good supplies for slayer (extreme strength and attack) as well as for boss hunting (overloads) while wasting money as little as possible. Cleaning herbs is almost never worth it, mixing your own potions can be if you have the herblore scroll. Really make sure you get that as it should save you millions and millions on the road to 99 berlore.
Use boosts in order to start making the untradeable potions asap.
Making every super potion will use a lot more money then making your most efficient potion, selling them, then buying ingredients for extremes.
Also make sure to get the herblore scroll from dungoneering, it will save you millions on the road to 99.
TL;DR Making supplies for untradeable potions will waste a lot of money. Make your most efficient potion then buy supplies for extremes.