As with most questions about servers experience every answer you’re going to get is totally subjective. Take anything we say - myself included - as an just an opinion. In the end you’ll have to test the waters yourself.
IMHO TL:DR - In my experience there are more opportunities to rp than there is time to participate. There is no simple one-size-fits-all place to look for roleplay or style of roleplay on WrA. Quality matters more than quantity, and what that means to you will determine where you will find the most enjoyable rp and who you want to invest time in playing with.
1. The people who are on WrA are here because we enjoy it. Whether or not you enjoy it as well depends a lot on what you are looking for, when & where you are looking for it. There used to be a few spots where there were almost always roleplayers standing around. Outside the Blue Recluse in SW for one example. These days where people tend to roleplay is a lot more widely distributed, so those older hubs aren’t as active as they used to be.
2. There are plenty of individuals, guilds and events that are supportive of new roleplayers. There are also plenty who have expectations which new roleplayers can’t necessarily meet.
My personal suggestion would be to hold off on committing to any particular guild - seek out individual players who are interested in helping. You will fond some who are even willing to sort of “chaperone” - help you enjoy events without being overwhelmed for example.
The Total Roleplay add-on is probably one you will want to install asap, for two reasons. First of all, there is an option for people to indicate that they are experienced roleplayers who are willing to help you. Secondly, you don’t have to fill out a character profile right away. You can put something in it to the effect that you are exploring what roleplaying like and experimenting to find out what works for you.
3. There’s the whole question of Quality vs. Quantity. Would you rather have a few very enjoyable opportunities to roleplay, or a ton of mediocre or even unpleasant experiences? Furthermore, it’s important to make a distinction between the statistics you can find on line about total character (not player) population, and how many of the players of those characters actively roleplay. There are no reliable statistics on roleplay. None.
If you watch the forum for any length of time sooner or later you will see “Horde RP is dead, only Alliance RP is any good” and “Alliance RP is dead, only Horde RP is any good” posted at almost the same exact time. That should tell you how subjective the answers to your question are.
In addition, right now may not be the best time to judge the roleplay community as far as numbers go. A lot of people temporarily stop playing during content lulls. So the available pool of potential roleplay partners is likely to be lower now than when 9.2 is released. There are also people who left because of the current Blizzard debacle(s) regarding mistreatment of employees. Some - but an unknown number - of the players who left are likely to come back.
Within the RP community on WrA there are a lot of cross-faction/neutral/non-aligned roleplay opportunities. This is an important enough part of roleplay on WrA that there are even what I would call “twinned guilds” - more or less the same group of players in an Alliance and a Horde guild which from the in-character point of view is a single organization. So if you are looking for friendly activities rather than confrontational RP then picking a faction probably isn’t as important as it once was.
4. There are definitely guilds on WrA very much focused on raiding. There also guilds which have both raiding and roleplay activities.
5. Shaureyne has a good short list. Coping with a lot of new add-ons all at once can be overwhelming, especially for trying out a new aspect of enjoying WoW. IMHO the single most important add-on for someone new to roleplaying is TRP. It lets you see who else is interested in roleplaying, gives you an idea what they are doing, how willing they are to help, and lets you help other people to know what you are looking for. Start using the other add-ons as you get more comfortable. Use the ones that the people you rp with are using.