Do you believe that the self 'truly' exists? Probably not.
The Buddha portrayed in the original (Pali) suttas say that any view about it at all prevents understanding.
Do you believe that phenomena 'truly' exist?
Personally? I don't have any beliefs about it either way. I report what others say about it, though.
If you think that they have momentary existence, then you should use your powers of reasoning to see if this is possible... if you are unable to show how phenomena can 'truly' exist then the Mahayana Sutras may help you to understand why e.g. Nagarjuna's commentaries on the Buddha's Prajnaparamita Sutras.
What's the difference between "existing" and "truly existing"? Also, if you're making/supporting the sunyata doctrine, then it's up to you to present a case for it.
If you'd rather not think about the emptiness of phenomena I understand.. the Buddha gave many teachings which avoid the need to examine it but they don't show how to become a fully enlightened Buddha or to help others in a way only Buddhas can.
I'm fine with the original concepts of anatta, anicca
and pattica samuppada
. If focusing on Nagarjuna's ideas helps you more than focusing on the ideas presented by the Buddha, then go for it.
But when people present Mahayana sutras as equivalent or superior to the suttas made by the Buddha, even though they were written long after he died, then I'm prone to questioning that. They focus heavily on mysticism, worship and the supernatural, whereas those were not the focus of the early suttas. I'm currently writing my M.A. thesis on something closely related to this and am sitting on a stack of research done by scholars who take that claim to task. Gombrich, Kuzminski, Bett, Thompson, Reale...