Carry as many as you feel like drafting.
It really depends on who they are more than anything else. If you have two solid guys with secure jobs then that's fine. If you're drafting from the bottom of the barrel you need to carry more guys since some of them won't work out. In a 10 team league there will always be solid starters on the wire, so I'd probably err on the side of more closers rather than less coming out of the draft. So maybe three, with a list of watch candidates set as well so you can swoop in a grab guys when they break out.
Also, because we're talking hth, you also need to consider whether you might be punting that category (i.e. not even attempting to be competitive) or possibly even setting it as a real strength for your team. If you want to win saves every week then you'll probably need 3 or even 4 guys. My personal preference for hth is to carry more relief guys than normal, but there's endless ways to build a team.