If you don't read this series, you'll be missing some of the, hands down, best damned TrekLit ever put to paper, or eink, or lcd, or whatever your preferred media is.
If I were just starting the series or planning to reread, I'd start with the S.C.E.-Lovell
arc, the last of which is a direct prequel to the series, and then I'd move on to the series proper. None of these are technically required reading though, even the direct prequel.
If you're a fan of TrekLit in general and TOS specifically, you should love this series. Personally, I hate to see it end this year but, All Good Things...