IMO
more than likely that would be a bit overstocked, especially with the 2 tangs, actually you should ahve a larger tank for only one tang, simply just because of the fact that thye need alot of room for swimming 4+feet is best(some people do keep them in smaller tanks though), but you may want to consider 4 or 5 smaller fish instead of the 2 tangs
jsut for refernce, you have about 32 inches of fish listed and although this is just a general rule, you may be able to have as many as 25 max.!!, and that is providing that all is perfect and you are able to maintain it well, normal reccommendation is 1 inch per 5 gallons, but sometimes may be pushed a bit, but you do not want to exceed 1 inch per 2(and this is only if conditions allow you to go this far and maintain stability) and 32 in 50 is way ove rthat(you also need to figure the size of fish at maturity),
noe other thing, the powder tangs are not the best choice for newcomers anyhow
sorry so long
HTH