A few questions for returned player

[Niwashi]

I read SE are freeing up more estates from inactives.

They're planning to, but it's not implemented yet, nor do we yet know exactly how it will work. Once it is in place, though, you'd presumably find available plots the same way you do now, by checking at the Aetherite whether there are any that list a price rather than an owner.

I couldn't find any ways to transfer the gils between my characters as the mail system doesn't seems to work that way. Do I need to find a trusted friend everytime to do this or is there another easier way to do this?

As Enkidoh pointed out, there's no direct or simple way. A couple other workarounds if you don't have a trusted friend available to help you:

If both your characters are in the same FC and have access to full use of the FC chest, you can use that to transfer items or possibly gil between them. Make sure that it's ok with the FC leader and that you have that access, though. Particularly for gil, most FCs limit gil withdrawal privileges to officers only (or even leader only) to prevent new people from joining just to steal from them.

Another option, one that doesn't require special access like that, but which costs a bit in market board tax, is to sell stuff to yourself. To pass items to your alt is pretty straightforward, just put the item up for sale, switch to your alt, and buy it. Just be sure it's priced high enough that someone else won't come along and buy it instead while you're switching characters, but low enough the alt you want to buy it with can afford it. To pass gil to your alt, start with the character you want to receive the money, use them to place a single simple cheap item (typically a common drop like an animal skin or something) on the market board priced at however much gil you want to transfer. Then switch to your richer character who's going to provide the gil, and buy it.

presumably SE did it to try and stop gilsellers transferring their ill gotten gil around

Possibly, but if so, it was pretty short-sighted. Gil sellers have multiple accounts and plenty of characters active at once, so have no problem transferring gil around between them. Plus they also form their own FCs, so are presumably using its chest to accumulate gil from their farming bots to be available to whichever character is used to transfer it to their buyers. The restriction really isn't hurting them at all. It's only a hassle to legitimate players, ones who only have one account's worth of characters to work with, and want to join an FC for social or gameplay reasons rather than finding or making one that will give them item/gil transfer capability.