1. For the search, you need to go to (using demo dataverse examples):
1. For examples of the javascript to use you can look at the search widget (or even actually imbed the widget itself):
Widget code example:
and adds this to the button:
<input id="btnDataverseSearch" value="Find" type="button" onclick="window.open('
https://demo.dataverse.org/dataverse.xhtml?alias=harvard&q=' + this.previousSibling.previousSibling.value + '', '_blank');" style="-moz-border-bottom-colors:none; -moz-border-left-colors:none; -moz-border-right-colors:none; -moz-border-top-colors:none; background-color:#f5f5f5; background-image:-moz-linear-gradient(center top , #ffffff, #e6e6e6); background-repeat:repeat-x; border:1px solid #ccc; border-color:#e6e6e6 #e6e6e6 #b3b3b3; border-image:none; border-radius:4px; box-shadow:0 1px 0 rgba(255, 255, 255, 0.2) inset, 0 1px 2px rgba(0, 0, 0, 0.05); color:#333; cursor:pointer; text-shadow:0 1px 1px rgba(255, 255, 255, 0.75); padding:0.3em 1em; line-height:1.4;">
2. For the add, do you already have the select box of the dataverses working and it's just the button you need? If so see, above. If it's the dropdown, then that's (obviously) more complex. You would need to use an API to get the list of dataverses, in Json form, then translate the Json html select markup. I don't have any specific example on how to do that, but can try to help (or maybe someone else has already done it?)
Hope that helps!
Gustavo