You could have a local block explorer that you could make calls to with php... save to the db.. then use a websocket server to keep the website live.
That would be my approach.
Yeah, I guess the easies and probably most performant way would be to have a local bitcoind running on the server and make JSON calls to it. Since the transactions / addresses can all go into one wallet it would probably be the best option.
Only downside to this is that I need a lot of space on the VPS which will be expensive, since there is no bitcoind thin client, like an electrumd would be the optimal solution for this I guess.