25,000 IU's of beta carotene is plenty, anything more than that is too much and your body doesn't need it. Please don't be one of those who think that 'if this much will help, even more is better' because your body will only use so much and then the rest will be excreted in your urine. Same with the 'B' vitamins. They're all water-soluble so you will simply pass out of your body what you don't use, so even though taking a high dose of them really won't hurt you (aside from maybe an upset stomach and a bad case of diarrhea), neither will it do you any good.
As far as which ones are risky, Vitamin A can be toxic in high doses (which is why we take beta-carotene) and vitamin D also should not be taken by supplement. And I know I will get some disagreement on that but vitamin D is not a vitamin we need to give ourselves as we normally get all we need from the sun. It isn't a vitamin whose excess is passed out of your body like the B vitamins, it will build up in high doses. So unless you never go outside in the sunshine, cover your entire body up with clothes when you do, and slather sunblock on every inch of your skin, the sun will do just fine is supplying all the vitamin D you need.