The amount of experience for each level is the same for different skills. Details here:
http://runescape.wikia.com/wiki/Experience
21212
level 99 woodcutting.
Cut down trees.
No.
Rather than ask here what level is required for different logs, just look it up under the woodcutting skill. Click on the skill icon within the game - it looks like a vertical bar graph - then on the woodcutting icon - it looks like a tree.
About twice as long as it took you to reach level 87 from level 1. Each level requires 10% more experience than the previous level.
15,699
By gaining experience in a certain skill, usually by completing activites related to that skill. For example, if you cut down a certain number of trees, your woodcutting level would rise.
Yes. In general, a higher woodcutting level not only gives you access to better logs, it also lets you cut them faster.
This entirely depends on what level you are starting at and what you are using to train the skill.
Getting your woodcutting level to 60 and cutting yews.
well usually level 61 or 62 or higher, depens on how many level 100 woodcutters are on there