'More importantly, that outfit — is that a swimsuit?!' 'Yup. Doesn't it look cool? Feeling turned on~?'
Literal
''More-than-that, that appearance... swimsuit!?'' ''That-is-so [feminine-よ]. Cool is [confirmation-でしょー!?] Horny-feeling do~?''
A risqué comic moment. それより ('more than that, more importantly') pivots the topic. カッコ is casual 格好 ('appearance, look, getup'). イケてる is slang for 'cool, attractive' — from 行ける ('to work, be OK') + ている, evolved into meaning 'it's working/hot'. ムラムラする is a suru-verb from ムラムラ ('feeling sexually excited, horny'), a 擬態語 for sexual arousal. The whole line is teasingly provocative.