Free printable Roman numerals worksheets for numbers up to 1,000, written both ways, with an answer key.
Up to 1,000 a numeral can use all seven letters, and the hundreds join the tens and ones: 949 is CMXLIX, which is CM (900), XL (40) and IX (9). Each question gives a number to write as a numeral or a numeral to read as a number, and a one-page sheet never repeats a number.
Reading a long numeral goes faster in chunks. Split it where the value of the letters changes, read each chunk, and add them up. The subtractive pairs CD (400), CM (900), XL (40), XC (90), IV (4) and IX (9) are the chunks that need care.

All seven: I, V, X, L, C, D and M. M is 1,000, so it appears only for the number 1,000 itself.
CM, which is 100 taken away from 1,000. In the same way 400 is CD and 90 is XC.
Write the hundreds, tens and ones separately and join them: 900 is CM, 40 is XL and 9 is IX, so 949 is CMXLIX.
Yes. Choose 3999 under Largest Number in the generator on this page. 3,999 is MMMCMXCIX, the largest number the standard numerals can write, because a fourth M in a row is not used.