I think people here are trying to make sure the OP understands that making a lot of things in your map a func_detail does not positively affect performance, but rather would affect it negatively because more would probably be drawn. Sometimes people misunderstand that func_detail is a magic brush that somehow takes less resources to render. In reality, when the map is compiled it becomes an ordinary world brush. The only significant difference between it and a world brush is in Hammer where, as some have said, it doesn't create visleaves upon compile. This makes sense because func_detailed items are usually quite small and incapable of blocking a player's line of sight, and so for them to cut leaves is unnecessary. Sometimes it is beneficial to leave world brushes alone as the visleaves they create can help break up rendered space, and help combat light bleeding and unrealistic shadows, if they are touching another brush. E.G. A pillar or structural beam that sits against a wall.
But I think in an early alpha, a map isn't likely to have many items of fine detail that qualify. An early alpha is likely to be composed of mostly large blocks. Some examples of things that could be func_detailed are steps and very small ledges because they have no role in blocking player sight. The large blocks are best left as world brushes because they will block player vision and so it makes sense for them to cut leaves.
Since an alpha map is devoid of most fine detail, I do not think it necessary to build any hint faces, unless they are outside in large spaces. Area portals and areaportalwindows are very useful in doorways and passages but will not work unless they are enclosed by world brushes. I think, as soupcan said, those should be the least of the visibility optimisation tools you engage with.
There is also a lot to be said for building a map with visibility in mind. Long sightlines through multiple rooms/areas should be avoided as they cannot be culled if a player can see them. Using large world brushes to create environmental corners, U-turns and S-bends is very good. Also notice how in Valve maps, doorways sometimes do not open straight out in to an area, but sideways. If you plan these things well, you will find visibility optimisation easy.