Hi! These are very good questions.
Q> Can you tell me the difference / limitation between [DE and SE]:
A> Differences between DE and SE are described in Developer's Manual on page 6:
"[Desktop Edition is] Intended for use from desktop applications connecting either to Postgres or Greenplum. Handles distribution policies, able to work with Greenplums’ forward-only cursors, utilizes gpload."
"[Server Edition is] Intended for use from servers (IIS, SSAS, SSIS, linked servers, etc.) connecting to Postgres and Greenplum databases. Optimized for extremely large rowsets, supports two phase commit protocol (DTC enlistment), and provides better integration with SSIS." In other words, the Server Edition provides additional functionality, faster on large rowsets, and more scalable (uses different memory management algorithm).
Q> if I bought the licence, automatically I will receive free 1 year [Technical Support and Product Upgrade]
A> Yes, correct.
Q> If in the 2nd year we still want the Product Upgrade, should we buy the new version license again or just buy the [Technical Support & Product Upgrade]?
A> The "Technical Support & Updrades" would be a better option. It would allow support and upgrades for multiple licenses previously purchased by the company. If the additional "1 Year Support" is purchased for multiple licenses, please contact Support via e-mail, and we will mark all the licenses for the extended support.
Q> Do you offer a discount price if we want to upgrade for the newer version, but our 1st year [Technical Support & Product Upgrade] already ended ?
A> Please e-mail request for discount to Support. The policies change.
Q> For the Technical Support, can you share me the means of support and the SLA ? Ex : request for support via emails, and the SLA for solving / fixing a bug, etc.
A> Our preferable communication type is e-mail, but the forum and phone can also be used. We usually answer e-mails in 24-hours, and start troubleshooting issues within 2-3 days after report about an issue is received. Time that takes to fix an issue depends on complexity of the issue, and current utilization of our resources. In most cases bugs get fixed and small enhancements are made during 1 week after request is received.