How to design a practical and secure MAC scheme?
There are many ways to authenticate the contents of the disk.  The way you have described is reasonable, if you have a way to store the global sequence number in an authentic way (so it cannot be tampered with).

Another general approach is to look at the data structure that is maintained by the UBI to map from logical block numbers LEV($v,l$) to physical block numbers PEB($p$).  Then, add a MAC on all entries of that data structure, and when you read the data structure, verify the MAC.

Also it might help to use tweakable encryption to encrypt each block, with the tweak set based upon the block numbers.

Broader comment: I think you should start by reading about full disk encryption (FDE) in general.  I don't see anything here that is terribly different from the issues facing FDE on magnetic hard disks.  Here are some good starting references:


Disk encryption theory, particularly its discussion of tweakable encryption.
IEEE P1619/D16 - Standard for Cryptographic Protection of Data on
Block-Oriented Storage Devices
And, these three research papers on disk encryption
Do Flash memory (SSD) architecture impacts encryption techniques?


Do note that many full disk encryption schemes provide only confidentiality, not authenticity, so you'll need to go beyond what those schemes offer.

P.S. One last comment: you are forming the input to your MAC by concatenation.  This is fine if all of the fields are fixed-length values, but if they are variable-length, you may be at risk of a concatenation attack.