The burden always falls on the mono partner to come up to speed.
You have to read all the poly material, go to a poly approved counselor because it wouldn't be fair to make your spouse uncomfortable.
The things you listed ....new firsts ...memories ....opportunity costs with the family, don't sound like jealous items.....those sound like factual logistical items alone the lines of daily grind and the fun cake and ice cream. ( food apology offen get used too ).
To your question what are going to get out of it .... Standard answer 1) happier spouse 2 ) you might get some spillover sex ...from a natural kick start to his libido ....or to make things seemed balanced. 3) because of the issues and topics and the need to discuss said ....there might be a feeling of greater closeness. As a consequence better communication skills.