We waited a year to get our second one, mainly because our first bd was just that - our first; we wanted to give ourselves time to get the hang of things and I think it was a smart decision. We gained a lot over that year, including having learned from inevitable newbie bd owner mistakes, and we now have a good order to feeding schedules etc... If you are not experienced with having multiple hands on animals at once, then I would recommend waiting it out a bit, but if you feel like you've adjusted well enough to having this one and don't think you would be too overwhelmed with a second, then go for it. We love our two :-D
As for tank mates, I would definitely keep them separate. You'd be taking a risk housing them together - one that could possibly be fatal if an attack did happen, and personally that's not a risk we were willing to take with ours, for both of our dragons' sake. Not to mention the emotional turmoil we would have ourselves knowing we could have prevented it. (just my 2 cents)