Park hours at Universal Studios Japan vary greatly during the year. Generally, summer hours are 9 or 9:30 am to 8 or 9 pm. It is a good idea to check the park operation hours before going to avoid any big surprises, because some days it is only open until 6 pm: http://www.usj.co.jp/e/parkguide/calendar.html
There are several ticket options. The standard, 1-day pass is ¥6600 for adults 12-64, ¥5900 for seniors over 65, and ¥4500 for children 4-11. There is also a 2-day pass and a group pass. You can exit and enter the park, but must check at the gate to get a special stamp. You can buy passes at the park or in advance on the internet or at approved agents.
There is a Universal Express Pass ticket that allows you to go to a special priority entrance and reduce your wait time for popular rides. The passes are available at ticket booths, but only a certain number are sold each day, so might be sold out. You can get a booklet for either 4 or 7 Express rides. This is especially useful on holidays or weekends when lines are longest. Be aware, though, that many rides have a height restriction, so if you plan to skip those because of a younger child, the Express Passes may be a waste. Confirm the restrictions on the website before deciding whether to buy one. The passes are ¥3200 for 4 rides or ¥4900 for 7, no matter the age.
It is easy to get to Universal Studios by train. Take the Osaka Loop Line to Nishikujo Station. From there, transfer to the Universal Studios line which takes about 6 minutes to get to your destination.