It depends on how many runes are needed.
For example: For Wind Wave, you will need Air Runes and Blood Runes. If you have any type of staff of Air, you will need 1 slot. All other spells will need at least 2 spots, 1 Air/Element rune (depending on the staff) and the combat rune (Mind, Chaos, Death, and Blood). The only exception is Water spells, as a Tome of Frost can be used from dungeoneering, combined with an air staff and you will only need the combat rune.
For Ancients, You will need space for water runes, air runes, fire runes, soul runes, blood runes, death runes, and maybe chaos runes if you are level 50-72. The ancient staff is recommended or better (best is Staff of Light)
Another note would be if you only cast 1 type of spell, you only need 3-4 spaces (4 for Smoke, 3 for Shadow, Blood, and Ice).
Note you may also consider law runes to Teleport, or teletabs (teleports are recommended as you will already have runes)
Cosmic runes will be needed with normal spellbook if you plan to alch items.
Again on normal, if you plan to bind/weaken enemies you will need nature/body runes.
On Lunar or High Level Normal, you will need Astral Runes likely.
At higher levels, it is NOT recommended to use a staff of an element, excluding the Tome of Frost (As this is an off hand item)
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Depends on the individual. Some people use runes for divination. Others use them for protective magic.
You can use the Low Level Alchemy at magic level 21 using 1 nature rune and 3 fire runes. Then after you get to magic level 55 you can High Level Alchemy using 1 nature rune and 5 fire runes. Both are for F2P and P2P.
crafting runes at alters. Use runes ess at certain alter to craft those runes. Eg water alter you crft water runes.
Basically, yes. Different wands and staffs give different bonuses to "magic accuracy", with the result that you have a higher chance of causing damage, thus increasing average damage-per-second. This has nothing to do with saving runes. However, a staff of air will use no air runes for spells that require them; similarly, a staff of fire, water, or earth will save you the corresponding runes. Since the air spells only use air runes, you can cast them for free if you wield a staff of air. A staff of light, on the other hand, gives you a 1/8 chance to save ANY type of rune, so on average, it will save you 1/8 of the total cost. Please note that the basic combat spells - that is, most combat spells in the standard spellbook - are now fairly cheap - especially if compared to the time before the Evolution of Combat upgrade - since they use only elemental runes.
No staff will really MAKE runes; however, some staffs will SAVE you the runes when you use the corresponding spell. Thus, by wielding a staff of fire, or one of the more advanced versions, you will need no fire runes for any spell (for instance, combat spell, or high alchemy) that normally requires them.