sure. "companionable" npcs would be posted around in towns and whatnot. you pick them up with a quick convo and go for a walk in a cave. they could participate in encountered battles. the total experience from the defeated pokemon would be split, giving your pokemon only some of the experience form the battle. the npc pokemon wouldnt have to level up, but i guess they could if They wanted them to. companions could be barred from gyms or gym battles. i think itd be pretty cool...

Honestly, considering bandwidth and whatnot, i personally wont be too worried about the appearance of the buildings. simple wood siding does the job for me. that being said, i think itd be cool if you incorporated pokemon into the architecture, kinda like the romans. like you could have a pic of a sleeping persian in the street in front of someones door. or maybe some random npc has his favorite pokemon painted all over his/her house.