A 401k is money in an account that has been contributed by you and established by your employer. When you leave that job, you can move the money to a new account which is called a 401k rollover.
Hard to say for there are a lot of brokerage firms/banks you can roll the money over to. May depend on what kind of asset you want to invest that money in...stock then brokerage is probably better....
You can roll a 401k plan over into a Roth IRA. However, when you do so, you will have to pay ordinary income tax on the amount rolled into the Roth. Even so, a Roth IRA will usually perform better...
I had a client in the same situation. (I assume you are the person who took out the loan on your own 401(k) )
When the rollover took place, the amount of the outstanding loan was deducted...