A good rule of thumb is that banks like to see 3+ active / open tradelines, but there is no specific standard requirement. You could possibly add a verification of rent or utilities to show credit.
Thanks for asking the question before taking action. Sometimes what seems logical to most folks works against them when it comes to banks.
DO NOT close any accounts! Having credit is the key to getting credit. The best credit you can have prior to getting a mortgage are accounts with lower balances, appx. 1/3 their limits, and paid on time. This demonstrates you can live with temptation and are responsible.
While paying the accounts off by the end of the year is a laudable goal, it could well cost you. Rates and prices in todayâ€™s market have increased home affordability. Where things will be in 12 months is anyoneâ€™s guess, but should either prices or more likely rates increase, you may be at a disadvantage in what you can buy.
Whenever possible I prefer to meet with my clients as early in their thinking process as possible. If we are days, weeks, months or even years out, we can map out a strategy to position them for a great decision. I would strongly suggest you meet with a local lender who can discuss your plans early and advise you as to which accounts to pay down, and by how much before you proceed. You will need some down payment and closing costs too, so it may be wiser to save some of your money for these items, rather than be paid off completely.