before buying anything else, have u explored your zoom? play around with the settings (distortion/overdrive/eq/filters etc) & understand how it affects the sound with your existing setup. i'm still using my 10 yr old zoom & find is ok to get the sound i want. if you can't find it, then only consider to buy something

there is no rules in finding your sound. it depends on the songs u wanna play. for most rock songs, i only set basic distortion or overdrive & EQs. put wah-wah & u can play sweet child solo already