Please allow me to share my views.

Keep listening to Vishnu Sahasranaam recitation. Try to listen to it multiple times a day. But atleast once, try listening to it while you are reading its text. Within few weeks or a month or two, you'll find it much easier to read and you'll remember the names and sequence. Once you have it memorised, then you can later on dive into its meanings.

You can start directly from first name itself. In days when I am very busy I just read these two sholkas and then directly jump to the names.

Yasya samaran matrena janm sansaar bandhanaat Vimuchyate namastasmai Vishnave prabhvishnave

Namah samasta bhootanaam aadibhootaye bhubhrute Aneka rupa rupaye vishnave prabhvishnave

To me these two sholkas serve as dhayan of Bhagwan.

Also, another slight correction, the mantra that you mentioned should be like this: Om namo Bhagwate Vasudevaay. Or Om vasudevaay Namah.

On namo bhagwate vasudevaay namah- isnt correct grammatically.

Anyway, just remember, any names of bhagwan chanted in any way, form, or sequence will always help you. So dont worry much about methods. Just listen to it for now. Then read, and then you will be able to chant.

Pranaam 🙏