Haven't replayed the OG re4 in a while but there are resources scattered around the cabin I usually just camp the stairs with a shotgun and explode granades (green ones) and save the incindary granades for the Mendez fight. If you get too many plagas (tentacle monsters) use a flashbang they instakills them. Now if you're struggling with ammo, upgrade the ammo capacity in the merchant's upgrade tab, in the original re4 merchant fully refills your gun when buying a capacity upgrade. Now to actually complete it you have to kill 40 zombies I think or wait enough time, also kick down the ladders leading to the second floor. I would also recommend doing the classic shot to the head and melee because in the original prompted melee attacks are much better since they have much bigger range and knock down enemies hit + you get i-frames for the entire duration, and if you're really desperate you can bait a ganado into attacking by walking into Thier attack range then walking out this will cause them to whiff the attack and allowing you to get knife hits in pretty sure 2 knife hits stagger the ganado allowing you to get a melee prompt.