Firstly, you can actually bypass the 1000 character limit by posting a few sentences, then going back and editing the post and adding the rest – it’s to try and stop spam posts and flamming, like I just did.
I’m really sorry to hear you’ve been having such problems trying to update your subscription and stuff, but I think I can see the problem. From what I was aware SE doesn’t support Steam Wallet as a payment method for paying for your subscription, only if you buy the game itself on Steam.
And in much the same way, Paypal isn’t actually available as a direct payment method for your subscription either, the only way you can use Paypal is to pay for SE’s own virtual currency called ‘Crysta’ which you can then use to pay for your subscription. From what I understand Crysta isn’t available as a payment method in all countries so it’s possible sadly it’s not available for players in your country.
The only payment methods available for the game according to the official FFXIV website (found here) are a credit card or debit card, or a prepaid time card which you can either buy online or from certain retailers, or by using the aforementioned Crysta option.
As for forum access, the reason it wouldn’t let you access it immediately is forum access is an active FFXIV account is required to access it, and it requires you to assign a character to it and choose a class – this actually determines your posting access on the forum, the higher your in game level, the more posts you can make per day. And it should go without saying that if you cancel your account or subscription, you also loose access to the forum as well. Sadly there is no way around it.
Finally on the topic of your preferred login name having already been taken, sadly that is a fact of the internet now – no matter the site or service you’re virtually guaranteed that someone has long chosen and claimed a name you desire, which means you have to think of creative alternatives instead (I was the same, my preferred name was already taken too). Unfortunately there is no way around it, it’s just how the internet is nowadays. And the reason the system asks for your birthday and location is to ensure you’re legally old enough to use the service (under the Terms of Service you have to be at least 13 years of age), and that your location matches the region for your copy of the game (to stop players importing foreign versions of the game into other countries).
Anyway, this red tape seems insurmountable, but don’t get discouraged!