First of all, let me pray to Allah to make things easy for you and bless you with a virtuous hajj.
Tawaf al-ifadah is one of the most foremost pillars of hajj; as such, the hajj is not complete without it. Tawaf al-wada' (farewell tawaf) is considered as either a strongly recommended act or obligatory which if anyone fails to do it should be redeemed by a sacrifice. As for combining them, that is fine as long as you do it close to your leaving Makkah. According to the majority of scholars, one should delay it until his or her departure; according to Hanafi School, there is no harm if a person had to do some last-minute shopping. However, it is still most desirable that a person leaves immediately after tawaf al-wada'.
Having said this, I should point out: if you do postpone tawaf al-ifadhah in order to combine it with tawaf al-wada' then you need to know that you are not released fully from the constraints of ihram; you have achieved only the first release. The final release cannot be achieved except by completing tawaf al-ifadah as well as sa'y (if you are performing tamattu'). Therefore, you are not allowed to have conjugal relations until you have completed tawaf and sa'y.
By looking at your schedule it is best for you to do them separately; you are allowed to do it even earlier than the ritual of pelting the stone; you may head straight to Makkah from Muzdalifah, perform tawaf al-ifadhah and then go to Mina, and pelt the stone pillar. If you do so the mataaf will be less crowded.
Once you have done that, you can do tawaf al-wada' prior to your departure from Makkah. This option will be far more reasonable and convenient.