Let me give you some information that clears up a few of these questions.
1.The new SDK supports interstitials, direct deals and videos only. The banners and other ad units previously offered are not offered in the new SDK.
2.The old SDK is still functional, so there is no problem leaving the old sections running as they currently are if you do not want to update them.
3.The new SDK does not require the AppFireworks and Leadbolt SDKs to be integrated separately. The new setup uses the AppFireworks to deliver the ads via an API connection, hence you only use the API key when integrating and “inapp” as it will be pulling the interstitials. There is no need (or option) for calling other ad units.
4.The two codes you mentioned, one is to cache, and one to call the cached ad. Hence, you need to cache the ad first, then display using the second code (the calls cannot be made in the same place. Initial call should be on entry, and re-cached after than ad is closed, ready for the next call).