For halter, you need 5 GRAND champion wins (with competition) and 70 halter points. At least one Grand Championship must be as a 2yo or older horse. But you don't have to retire a horse from that discipline if you don't want to. I will be showing my new gelding in halter, and he's got 200 points and his HOF.
Also, this used to confuse me (so in case it does anyone else), the grand champion wins are the all-age championships. The jr. championships and sr. championships give you halter points but do not count as grand champion wins.