If you close with a title company, you don't have to worry about the 7k. It's their job to clear that and anything else that the seller might not know about from the funds that you bring to the table.
Be aware that purchasing his business and "absorbing" it into yours carries its own risks that should be addressed by a business attorney so that you don't end up being liable for things that happened before the purchase date. For example, even if you keep his employees and vendors, you'll likely be advised to start their payroll from scratch and also to open new vendor accounts, instead of assuming his.
My understanding (I'm not an attorney or accountant) is that the IRS considers single member LLCs to be disregarded entities, so there is no financial tax-related benefit to having two different LLCs. That being said, I suspect it will be beneficial for the following reasons:
1) If done properly, it can reduce your liability so that if one LLC is sued, the other is somewhat protected.
2) If you treat them like two individual businesses, it will be easier sell just one off in the future, should you choose to do so. Also, if you mix the books, your future buyer pool will be limited to people who understand both metalsmithing and real estate.