You have mulitple options.
1. AS you described in the question, buy two 50 bundles will let you have a publisher with 100 user license, and a subscriber server.
2. Just buy one starter bundle, and use the MCS server as you back server. Please check the MCS server is supported in 9.0. In this case, you will need to upgrade the MCS server with 9.0 SW.
The migration program includes mulitples parts:
1. Migration bundle is discounted with its price just around $1K higher than the listed bare metal server price. and with pre-loaded OS and VMware. It also comes with the free VCS licesnse (5 travelsal license + 10 non travesal ), 5 CC agent license and required VMware license.
2. Don't need to purchase new license. Just migrate them. What really matters is the migration discount on license. With the 9X3 migration promotion, you can migrate you licesnse to BE6000 for $9 per license if 3 year UCSS is purchased.
3. Use the MCS server as reducndancy server or run other applications.
4. You don;t nee to upgrade to 9.0 first ro be able to migrate.
We are going to publish a white paper for migration ery soon. Please stay tuned.