RE: obstacles, think of it like what you’re saying in the spell section – there’s enough weird shit happening in D&D that they’ll be able to figure something out. Or even just avoid the obstacle entirely.
For rewards, the grenades sound great. I love giving people weird little things that aren’t in any official book that they kind of have to figure out. I deal with the money problem by using carousing rules – players spend money in “safe” towns to gain XP, with a chance of bad or just weird things happening as a result. There are plenty of carousing tables and rules out there if you poke around, find the one that makes the most sense to you or roll your own, if it’s a paradigm that would work for your group.