The IRS limits annual contributions to an IRA. Go to the IRS website where you download the publications that detail all the guidelines and restrictions re: IRAs.
You can basically put up to 50% of your inheritance into the IRA if you would like to. There is no set number, but I suggest you should not put all your funds into IRA.
You can contribute as much of it as you want to your IRA. IRA accounts are usually used as a tax shelter as well as an investment vehicle. You do not have to pay taxes on inheritance monies so you may want to find a different investment for this money.
You can only contribute to the maximum contribution limit. For Traditional IRA, that's $5,000 / yr, plus another $1,000 year if you're age 50 or older (catch-up contribution).