Hi.
When i speak of caring about characters I wasn't thinking a full on novel or gamebook, just some reason for why your doing what your doing and an actual plot with progression and events in the world, not just "you are insert name the insert class, go into the dungeon and slay lots of things"
On a basic level look at something like Legend of Zelda. Link never actually speaks, yet people grow attached to him just because of the various things he's asked to do and what he goes through from being chucked into the dark world to being catapulted through time. For something even more so look at secret of mana (one rpg I'd give my back teeth to play). You pretty much just wander around from area to area, all npcs just have one peace of dialogue in each area, (occasionally two, pre and post dungeon objective complete), but still the plot has huge amounts of prominance and your characters actually have personality.
There isn't a need for anything too complex for this, just npcs who speak, and the odd text description of an event when you wander around the map. For example, (to take something very rough just out of my head), you begin the game and are told to go and fetch water from the well in the wood, kew first dungeon and explorable area. You get back to the village and find everyone is worried about the evil empire invading (buy your first weapons and get your first gear), and that the high priest at the temple wants to see you. when you meet the priest he tells you about magic and how the tiny island they're on is protected from attack by a magic forcefield, but that the forcefield is old and needs renewing, and that the power source for the forcefield is in the old mine.
kew second dungeon. Finishing the old mine you meet a spirit that explains it was trapped by the villagers long ago to power the magic force field and keep the village safe, but that it wants to leave. Your character decides to free the spirit and let it go, however when you come out the village has been attacked by the empire and lies in ruins (it's not a propper rpg plot if your little peasant village doesn't get destroyed at the start of the game is it).
All this is possible with npcs on the map you can talk to with just one peace of dialogue, no need for choices etc, however already in my littel miniplot I've established your character as a nice person, if a bit of a dope, run through two dungeons and introduced some bad guys.
As regards additional content, I didn't realize you were planning on creating an actual rpg with plot, rather than something more similar to a rogluelike. In that case, then probably your best off with not allowing people to add to it sinse manifestly it's your own world you are creating and you don't want too many different people flavouring the game differently. Though you might hav say an extra game plus mode or some zones specifically for people to add additional content away from the main plot and areas of the game.
As to combat, one of the general problems with audio games is that they can too easily turn into a boppit game, where the player just reacts to specific sounds rather than making judgements about a set of game factors, for example if your typing "dodge" everytime you hear the enemy swing their weapon. I also wonder how easy it will be to check your health, mana etc if your having to type in commands mid battle.
I like the idea of pausing things to read descriptions both of the enemies and of any specifically nasty attacks, however I do wonder if this should be something the player controls, for example if the game could track when sapi or the screen reader was speaking and pause combat accordingly, then the player could just hit control to skip what descriptions he/she didn't want.
Thinking about it, one thing you might considder is to separate out physical combat and magical combat, and have one be real time, and one not, rather the way combat in secret of mana worked.
So, physical attacks all have standard sounds as the enemy targets different bits and you have to parry, repost or wind up attacks beatemup style with correct key presses, say r then up arrow to repost high, p then right arrow to parry an attack on your right etc. When magic or other special attacks are used however you hit tab to bring up the console and type in "Cast fireball" or "giant slash" or whatever, then you cannot attack physically for say half a second as your big attack happens (though the enemy obviously can), and there is an escalating rising tone, when that tone hits the top, the action pauses and you get the sounds and description of the magic/special hitting.
Ditto with your enemies, if they use a magic or special attack, they stop attacking physically and you hear the wind up sound where you get some free shots in, then the wind up stops and you get the description of what they do along with the sound.
By having tab as the pause and bring up console key, you get the best of both worlds, an intense physical action affair where your needing to use real time fast maneuvers agaisnt the enemy, and as much magic or specials as you want, but ones which must be used sparingly.
Edit: to answer your final question, turn based combat is based on the idea of slowing things down enough for you to take significant actions, it is not supposed to be realistic in temporal terms.
Think of a fencing match. You swing your sword, your opponent blocks and goes for a parry, you dodge the parry and repost. Turn based combat is based on this idea, that your actions in a fight are a direct responde to what your opponent does and visa versa, it's just that in a game the turns are slowed down enough to discuss and considder with reference to the game's tactics, where as in reality they would be much quicker, and only a highly trained person would be cool enough to sit and considder tactics in a real life or death fight.
The advantage is that you can both include atmospheric descriptions and deep combat tactics, which is why games like final fantasy have gone on for years being turn based, rather than turning into beatemups.
Unfortunately many representations of turn based combat do indeed just become "you ihit it" "it hits you" which is both dull and unrealistic, but if you get it done properly it can work very well.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)