I agree that Visual Arts will be rather challenging for someone without prior experience or a love for the arts. It is not a 'filler' subject. The subject is extremely time-consuming near final exam time. You don't want to be still doing coursework when everyone is hunkering down to study for final exams.
Of your 3 HLs, a HL English is certainly a "must" for Law in the UK, so you are good. Doing HL History is typical of applying to Law too but it is not 100% essential. Never take a subject that you have no confidence scoring well. History is one of the hardest subjects to score a 6 or 7. With law, you need a minimum of 666 (you will not likely get an offer) from all your HLs. I have friends who didn't take HL History but HL Econs and HL Global Politics, and they had offers from Durham, QMUL, Warwick and KCL.
In the UK, LNAT score is heavily weighted in the universities' assessment, unless it is a university that does not require the LNAT (maybe you want to apply to some LNAT universities and some non-LNAT universities as your safeties). You can google for the various minimum LNAT score that each of your university choices require, and hope to do well in LNAT and obtain above the threshold. A friend was rejected by UCL because her LNAT score was not as competitive.
I don't think law schools have any minimum math subject requirement but SL Math AI is seen as a weak subject. If possible, take SL Math AA.