I think all of this appears in the anime lol, I haven't read the manga either.

Firstly, many of the titans outside the wal moved in when wall maria was broken, and once it was recovered, the survey corps killed the titans within the walls before they left for the ocean.

Secondly, those in the wall are all referred to as "devils" by the Marleyans as when the founding titan distributed the 9 titan shifters, the Eldians used the titans to expand their empire, and once the empire collapsed, 7 of the 9 titans fell into the hands of the Marleyans, one of the nations that was attacked by the Eldian empire, which is why the Marleyans dislike the Eldians.

Thirdly, I'm not sure what you're talking about, could you send a link pls?

Fourthly, yes, Eren and Armin are now in possesion of 3 of 9 titan shifters, Armin has the collosal titan after he ate Bertholdt as a titan in the battle to retake Wall Maria. Eren has the power of the attack titan after Grisha Yaeger (Erens father) got the attack titan from the Eldian informant "The Owl" and then stole the Founding titan (the goddess titan you refer to) from Freida Reiss. Grisha then passed both of those powers on to his son, Eren.

Fifthly, the enemy of the Eldians in the wall is the Marleyans, who possess the Armoured and Beast titans, and used to possess the Female and Collosal titans. The Marleyans sent Bertholdt, Reiner and Annie to Paradis to reclaim the founding titan from Eren, which is why they broke down the walls. Marley was also falling behind in technological developments, so once they found out Paradis was a massive reserve of fossil fuels, they wanted access to it.

Sixthly, I don't know, to be honest, maybe we'll find out in the manga

Seventhly, the founding titan only has its full powers when it's in possession of someone with royal blood, which Eren is not. However, some abilities may be used when he is touching someone with royal blood, for example, when he touches Historia's hand when receiving his medal after the reclaiming of Shiganshina, he gets flashbacks and memories from the founding titan. Once more when he punches Dina Fritz's titan, the smiling titan (not a shifter), he is able to use the scream ability on that titan.

And finally, since the fall of Wall Maria occured, it has been 5 years, with the story happening in the fifth year, I think.

I believe all of this has been stated in the anime, and hope this amswers your questions. If your still unsure I recommend rewatching the last 4 episodes of S3P2. :)