Hi Steven,
1. Correct. Currently restricted from EHP7 but soon you shall see the Direct installation package for EHP8 and more upgrade paths being made available with more latest SUM PL which will enable you to move to EHP8/NW7.5 directly. Notes shall alse be updated with the changes.
2. This is strange. Solman 7.1 SPS5 or higher is the only requirement for you to see EHP7.
Could you please check your LMDB/SLD for correct technical information of the system you want to upgrade with correct product version and components?. Try to resync the technical system from SLD again. Also, please provide screenshots so that we can take a gander and advice what could be wrong.
3. Maintenance Planner should be a breeze of fresh air for all. It has many advantages and simplifications that you will see when you get to using it. There are zero preperatory steps. Its a hosted solution provided by SAP directly. You only need S-User to access and launch it directly on portal. It brings a host of simplifications and improvements along with new UI experience. It combines all tools -- Upgrade dependency analyzer, Product system editor, MOPZ under one umbrella.
Just launch it from the link in here and see for yourself ---- Your systems may already be there depending on whether they are being updated to the Support portal for EWA etc.