Can someone please inform me the ammount of posts or what it is you must do to reach each rank as a member. Meaning the Junior Member which I am, and Senior Member and so on and so forth. I've been playing LoL for quite a while now but just haven't been very active in the forums but am wishing to change that and get away from this Junior buissness.

I believe 100 posts.

30/100 for member/senior member. That said, don't spam posts to get your post count up, because by and large people ignore titles, and if you do spam it could result in punishment.

Do not worry about your title. It does not reflect much in the way of how intellegent you are or knowledgible you are on a particular situation.
The easiest way to earn the titles and gain a decent reputation is to look at the forums, pick a few that you like going to. From there, read the titles and skim a few threads seeing what they are about. If you do wish to post, think it over a bit and see if it will past the captain obivious test and the smarty pants test, then you can post it.

Does this count as spamming; I just post in bursts because I forget about the forums from time to time or I've already posted my thoughts on a topic and then I check after a few months and find new ones all at once.

Responding to a thread that has been dead for months is known as necroposting and it is frowned upon just about everywhere on the internet. People may take the time to read the whole thread—and even write a response—without noticing that the dates are from months in the past.

If you read a very old thread and want to talk about that topic, don't bump it. Just make a new thread on that topic. If necessary, you could quote the old thread when you make the new one.

It doesn't really matter, I mean, you can't find out how many posts you have created anyway.