As far as roads, I don't think adding them in would be necessary. But since it's most likely going to be a purely aesthetic addition, it doesn't matter either way. Do them if you want to. I don't think it would clutter it too much, but of course, we'd have to see it to know for sure. Either way, up to you.
I don't think it needs trees either. I think the Alamo walls and the river is enough for impassables. Plus, you're right, it was pretty open as far as I know, not many woods and the like.
The commanders look okay. You may need to replace them or polish them later, I don't know.
Some thoughts on the commanders:
It seems odd that there are only 5 Mexican commanders but 6 Texian commanders. The Mexican force was something like 2-3 thousand troops, while the Texians had something like 300ish troops. I understand the reasoning for having all the commanders, since it's part of your bonus structure, but maybe some other way can be used to keep the bonus structure but still get rid of all but maybe Crockett, Bowie and Austin. And they should be in the fort, not on the outside. It wouldn't make sense to try to defend the fort from outside of it. Maybe you can expand the Alamo just a little bit, maybe by making the surrounding areas (Wharton, Austin, Bowie, Dickenson) slightly smaller. Then there could be room to have 3 different sections that would fit a commander each. Or something. But it does seem odd that such a larger force has 1 less commander than the Texians.
As for the auto-deploy situation, I would think all the commanders should have an auto-deploy. Making Santa Anna and one of the Texian commanders as a +2 though to signify that they were the leaders makes sense as well though. I would lean toward making the +2 Texian commander Austin instead of Bowie. While they shared command of the fort, Bowie soon relinquished control to Austin since he was confined to bed because of his illness.
The cannons...I would get rid of the cannon in Duque's area and put it in Morales' area. I would also take one from Santa Anna's area and add it and maybe even an extra one to Cos' area, since the cannons were placed to the South, East and Southeast if I remember correctly. It didn't mention anything about cannons to the north. Should probably also add a cannon in the Alamo on the south wall, since there were some located there.
As for graphics...just keep working on them. The borders still need work. The walls still need to be corrected, with palisade in the Northeast/east and south central areas.
Overall, nice improvements. Still lots of work to do, but it's getting there.