Most of the FC Halifax Town fans hate Halifax RLFC with a passion (they still believe that we're squatters at the Shay). The move to the Shay probably wasn't the best managed thing that's ever happened, and there's still a large degree of lingering animosity between the two clubs as a result.
What I can't believe is that any FC Halifax Town fans would pay an entrance fee just to have a go at you. You'll be in the North Stand, and tbh, I'd think they'd be more likely to go in the South Stand with the Fax fans if they really want to cause any trouble. Just be careful if you choose to go into the town centre before or after the game for a beer.
There's plenty of on-street parking around Halifax, but make sure you read the signs, as some of it is resident-only on a Sunday. Not much available in close vicinity of the Shay, but if you don't mind a 10 minute walk then no problem. That said, the multi-storey car park that Malfax advertised is a safe option, and a very short walk to the turnstiles.