1) A Paladin would need at least 24-27 ranks to inscribe one of his own spells on his weapon right? Blessed Hammer for example. With less ranks he can?t scribe any spell from his sphere right? Just confirming.
To scribe Battle Runes from Universal Sphere costs number of ranks equal to 5 + PP cost of spell.
To scribe Battle Runes from Other Spheres costs number of ranks equal to 20 + PP cost of spell.
Martial Law does not list any Paladin spells as being capable of being used for Battle Runes. it would be up to the GM to determine which spells are usable and which aren't.
2) Rune activation: its stated there that the character can activate more than one BattleRune at the same time. In the example: "Nynyve announces that she is activating the following Battle Runes: the Boost Agility Rune on her Armor, and the
Fireball on an arrow. She also announces that she is moving into a good position for her bow." So Activate a battlerune is like just speak a magic word, touch a part of the armor, meaning its a free action and you can move at the same time for example?
Yes
3) Costs: Its not stated there how much should cost the materials. The original idea is that monerary limits to materials shall not be as issue right?
Material doesn't matter. The character may inscribe the Battle Runes on any piece of armor or weapon, with the limits on the number inscribed per item as given.
Remember, Battle Runes only last 24 hours and then fade on their own. These are NOT like normal runes, they do not last until cast.
4) This sentence confuses me:
"For every 20 ranks a character has in the Battle Runes skill, he or she can add one of the following options to the Battle Rune:"
This means:
1-20 ranks = 1
21-40 ranks = 2
and so or or....
1-19 = 0
20-39 = 1
40-59 = 2 ?
For every full 20 ranks you have, you can add in one of the options. These are not ranks above and beyond what is needed scribing the rune, but use the same skill, just counting the ranks separately.
Same aplies to: "A character can inscribe one Battle Rune for every 5 ranks he or she has in the Battle Rune Skill."
Okay, say you have 23 ranks in the Battle Runes skill.
This means that you know how to inscribe 4 different runes (whether or not you have enough ranks to actually inscribe the rune is a completely different story, as in the case of Paladin Base spells that you GM might approve of).
Having 23 ranks also means that you may apply one of the options to any rune you inscribe.
You may also inscribe the 4 runes you know up to a total of 23 times (in any combination, not each).
So if I am reading it right BattleRunes is a powerfull but extremely expensive option. Its a skill that you need la ton of ranks to actually do something usefull with it (even so only base form spells).
For Universal spells, it is more useful than it is for spells from a Specific Sphere, but the whole idea is to give non-spell users a boost without requiring them to actually learn the spells and so forth.
A character will need to be third level (and maxed out in ranks) at the very least before this skill actually becomes useful.
I hope that this answers your questions...