Mishnah chagigah 2:1
מה לפנים ומה לאחור does NOT mean one should not think about olam haba! See rashi and bartenura there; it means either what’s past the world to the west(lifnim meaning east) or before/after the creation of the world, what was before bereshis and what will be באחרית הימים , but in ways that do not bring one to yiras shomayim, just academic contemplation.
It doesn’t say “woe to…” It says it’s better for such people not to have been born, since they are likely to fall into apikorsus.
Conservative Judaism invented the idea that judaism is about this world. They minimize olam haba, and you probably heard this from one of them or someone who grew up conservative.
Torah Judaism is very clear on what we’re here for – mishnaj avos 4:16, this world is merely a corridor to olam haba. We will experience the perfection we aquire in this world through Torah and mitzvos in olam haba; it is what we were created for – Hashem created the world to give us olam haba, through the torah. See mesilas yeshorim perek 1 for a more elabore description, where he says that no one logical can think that we were created for this world, as it has so much suffering…why would a merciful God create us mainly to suffer and then there’s this vague unknown thing callee olam haba that we don’t really know much about…..
No. We know just what olam haba is; it is the closeness to Hashem that we merit, tzadikim yoshvim, the righteous sit and enjoy the splendor of Hashem’s schechina, the more righteous, the more reward.