A silver aro will get to 3 foot long thus your tank can only be considered as temporary accommodation, and you'll have to upgrade fairly soon. Yes, you can add add driftwood and plants, a few floating plants may give the aro some cover and a sense of security. Leave the top of the water free for swimming. Loaches, catfish are all good tank mates, if they can fit in the aro's mouth they may become snacks. Silvers grow fast, 2 - 4cm per month, so potential tank mates will have to keep up with that growth rate.