Although not a pro, I'm not a fan of PEX either.
One thing to consider -- even though fewer joints is less to go wrong, you can always prefabricate sections before installation to get the in-place joints where you want them. For example, if you can get the riser out by undoing the union (background pipe in second picture) then you can get a copper section in just like it...
Also, they make those fabric heat shields. If you can't afford that, even a couple layers of aluminum foil behind the joint can help some, with the added benefit that it will warn you by a noisy crinkling sound and melting just before the wood catches on fire. Have a good bucket of water and extinguisher handy.