I assume you are talking about the Battle of Vienna in 1683, not the sieges in 1529 or 1485. As the historians from Wargamer have stated here previously, western uniforms changed quite a bit between the time period in BFAS and the 1680s and the official Imperial figures are not really suitable, so you would need to look elsewhere for "Wars of the Grand Alliance" style figures.
Then there is the prospect of gaming sieges, which is more suited as a campaign boardgame as the besiegement lasted more than two months. Miniatures games usually center on actions outside the walls or just the final assault. Since the decisive action was the battle on 12 September you could get away without siege rules, using only the walls mostly for decoration. However it was a huge battle with almost 250,000 men, which is way outside the scope of BFAS Division level. So until Wargamer releases Level III/IV rules you must either limit yourself to minor parts of the action, scale down the size of the battle ("bathtubbing") or find another ruleset of more epic scale. Still, people have attempted to recrate it in miniatures several times