10mm is a good choice....more safe....personal opinion min 8mm....but your tank only 1.5ft....so no need 10mm...the pressure in the tank not so great....30-40kgs of LR should be enough....depend on what kind of structure u wanna your tank to look like(Bt Timah Hill or Mt Everest)....get it from Sea Life in Balestier....maybe still got LR sell....Kent Salt is the recommended salt....it has very good buffer abilities....well any type of filteration system also can use....canister also good lar....all depend on individual preference....jus like car....some prefer Toyota, some prefer Nissan....some die die also want Ferrari....all depends what you want as all serve the same purpose. OF is the highly popular choice among marine aquarist but if no OF means cannot keep marine fish meh?i think more important is the frequency of maintenace, type of filter media used etc