It depends on the time of day. In my (limited) experience, you often have to change at Osaki if you travel late evening, for example. It's not a big deal to change there, although I think you have to cross to another platform.

Going to Tennozu Isle is your best bet but the monorail station is not directly connected. You have to go outside and cross the street. You might just want to take a cab to Tennozu. It should be only 810 yen, the minimum fare.

Use www.jorudan.co.jp to check schedules.

Google maps works well too unless there are schedule changes like just after the earthquake. This could possibly happen later in the summer due to electricity conservation. I have found that it's been correct in recent weeks. It's very easy to use with the Iphone (or other smartphone), but as a tourist maybe you don't want to pay for the data charges.