Multivitamin AND D3?

I mean, how much D is in the multivit and then how much is in the dedicated supp?

Where I work (a Canadian health charity), we suggest the following for all adults in the general population: "consider taking up to 4000 IU supplement of vitamin D per day during the winter or if you are at risk of low sun exposure. The risk of vitamin D toxicity is extremely rare, however, with supplements, there is the potential that vitamin D could build up to toxic levels. Supplements taken as directed and up to 4000 IU/day for adults would not lead to toxicity. This is not intended as medical guidance, so it is recommended that you speak with your physician about appropriate levels of vitamin D intake."

Bold emphasis is mine. If you're staying indoors more often than usual and concerned about your D intake (aha-haha-ah-ha), then that's also a reason to talk with your healthcare team.

Those amounts are generally regarded as safe but if you are unsure, check with your PCP.