If I am 35 yrs my husband is 45 yrs, and we are planning to have a first child, what are the risks involved?

Every pregnancy does. There are about 4% of all pregnancies, regardless of age that end in an unexpected outcome. Prematurity, sick infant, cleft palate, Down syndrome, etc. As you approach 40 you add 1% to the DS risk, 45, 2% and so on. For specific risks you can consult with a medical geneticist who will evaluate both family trees for potential surprises.
Genetic issues. The older the members of the couple are, the higher the risk of genetic defects such as down's syndrome. You also have the ordinary risks of your genetic inheritance if you both carry common defective genes although this is small. 35 years is still young enough not to worry too much. You could get tested but this is only reasonable, if you plan to do something depending upon results.