Hi
As Jo says, there needs to be clear evidence as to the existence and amount of the debt, as with any other creditor. I don't think we need be concerned about how the debt arose.
To answer your points:
1. He does have the right to vote and is just as entitled as any other creditor to receive a dividend from the arrangement fund. However, it might be considered to be a good strategy for him to agree that his entitlement to dividends be deferred in favour of unconnected creditors i.e he doesn't get paid anything out of the IVA until other creditors have been paid in full. This would be a smart move if you are on good terms. There are specific rules governing cases where associated creditors vote on arrangements, designed to prevent an associated creditor steamrollering approval against the wishes of a majority of unconnected creditors.
2. On the basis he is a creditor, he is entitled to a copy of the full proposal, the statement of affairs, and all ancillary documentation received by all the other creditors. Given that the nominee has a legal obligation to notify all creditors of whom he has become aware, the only way you will get round this rule is for your ex-partner to formally waive all rights in respect of the debt prior to issue with the proposal. You could elect of course to exclude your ex-partner from the proposal, however because of the obligation on the nominee he still requires a copy of it. Additionally, as excluding him from the proposal will mean he will not be bound by it, it is realistic to expect an adverse reaction from all your other creditors.
3. This point has been the subject of much debate on this forum. see
http://www.iva.co.uk/forum/topic.asp?TOPIC_ID=8705
and in particular see the final post of Melanie Giles setting out the income reviews required by proposals issued under the forthcoming BBA protocol, which takes effect on Friday.
Hope this helps
Ian