All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
First of all, may Allaah greatly reward you for being keen to gain lawful earnings; this is indeed what a Muslim's concern should be. Verily, there are blessings in lawful earning but there are no blessings in illegal earnings.
As regards the work of your husband in an auto-leasing company, in principle it is permissible if the nature of his work has nothing to do with any forbidden matter that this company might deal with. The fact that this company deals with a bank has no effect on him as long as his work is as mentioned. However, if the nature of his work necessitates dealing with what is unlawful or helping what is unlawful then it is not permissible for him to work there; rather he should abandon his work, it might be that Allaah will facilitate his affairs if he fears Him.
As regards migrating to a Muslim country, then this is an obligation if this is possible. Even if there are some unlawful works in Muslim countries, yet there are many lawful jobs in addition to many other benefits like being far from the means of being tempted and afflicted as these are so many in non-Muslim countries like the existence of illegal means of provision and what incites to it.
As regards Zakat, if a Muslim possesses a minimum amount liable for Zakat and a whole lunar year elapses on it, he has to pay Zakat. He has to pay 2.5% for any gold and silver and other cash money. As regards voluntary alms, one can give anything from his wealth; may Allaah accept from him. This is of course if this wealth is lawful as Zakat is not obligatory on unlawful wealth, and it is not permissible to give alms from unlawful wealth with the intention of getting closer to Allaah, as Allaah is Tayyib (which implies purity) and He accepts only that which is pure. It is forbidden for a Muslim to benefit from illegal money; rather he should spend it with the intention of getting rid of it.
Allaah Knows best.