Please do what you think is best for your spiritual journey, Alaray. Frankly, there is no ambition here to convert you to secular buddhism, of which there are many kinds depending on how one defines secular, but even then its just a convenient designator and nothing more, not even an identity. If Theravada feels right for you, go for it.
As per the matter of rebirth, as not to beat a dead horse, as a ‘secular or agnostic’ I adopt a psychological interpretation focused on the arising of the “I”, craving, and “self” in this life and neither reject nor pick up the literal interpretation. I don’t say it exists and I don’t say it doesn’t exist. I don’t worry about if there were past lives or if there will be future ones. There are no anxieties or expectations on the matter.
Since it is the longing and the craving that causes the suffering, in practice this means I strive to end longing for rebirth or craving any future state of existence, especially in this life, irrespective of whether literal rebirth is true or not.
Some passages I will end with.
"Nothing has been grasped by [me] from among the doctrines, after consideration, saying “I profess this”. But looking among the doctrines, not grasping, while searching I saw inner peace…
“Those decisions which have been formed”, said Magandiya, “you speak of indeed without grasping, sage. This thing (called) inner peace, how is it proclaimed by the wise?”
[Donabedian’s note, when asked about inner peace, Gotama speaks of purity, so likely in this passage purity connotes the state of peace, that is a completely pure state (ie. nothing but peace).]
“One says that that purity is not by view, by learning by knowledge or even by virtuous conduct or views” said the Blessed One. “Not by absence of of view, of learning, of knowledge, of virtuous conduct, or views, not by that either”. “And discarding these, without grasping, calmed, not dependent, one would not long for existence”
If one says that purity is not by view, by learning, by knowledge or even by virtuous conduct or views" said Magandiya. “nor by absence of of view, of learning, of knowledge, of virtuous conduct, or views, not by that either, I think his doctrine is foolish indeed. Some do believe that purity is by means of view.”
"Dependent upon view, inquiring, Magandiya, said the Blessed one, "You have become infatuated in respect of what has been grasped, and hence you have not even the slightest notion. Therefore you regard it as foolish. "
Whoever thinks himself equal, superior, or inferior, he would dispute on that account. But one unshaken in the thee modes of self conceit- for him there is no “equal” or “superior”.
Why would that Brahman say, “It is true.” Or with whom would he dispute, saying “It is false”.
In whom there is no idea of being equal or unequal either, with whom would he join in dispute?
A great man would not grasp and dispute about those views, free from which he should conduct himself in the world…
There are no ties for one who is devoid of perceptions. There are no illusions for one who is released through wisdom. But those who have grasped perception and view wander in the world, causing offense".
- Snp 4.9, Norman translation