I have never made a multiplayer map before, so I need some advice on the placement of weapons and spawn points.

How many spawn points should I have for a fairly large map? To give you some idea, it takes approximately thirty seconds to walk from one side of the map to the other. It has four levels, plus a basement.

Should I place the spawn points as far apart from each other as possible? Should I place the weapons and ammos far from each of the spawn points? Is it better to place the healthkits and batteries away from the weapons (or is mixing them in the same area reasonable)?

I know it's essential to create a natural "flow" in a deathmatch arena, placing items in spots to encourage movement for each of the players. It's also important not to place any heavy weapons near any of the spawn points, so that no one will dominate over the other players.

I tried timing myself sprinting from one spawn point to the next battery/weapon location to ensure that each of the spawn points is not too near/far from the closest goody cache.

Anything else I've missed?

It is not important for weapons to spawn out of sight from eachother, but it makes the map better if there is one weapon per room, or in a big room, one weapon per corner. If you have one room that has the shotgun, rpg and the smg in it, and there are rooms that have nothing but prop_physics, then move some weapons to the other roooms.

If someone goes into the "weapon room" and theey run out of ammo they just have to walk over the respawned weapons and they have ammo again, but if there is only one wepon around it gives the appearance of having nothing left to give in that room,(because the weapon they picked up is gone and there is nothing else there weapon-wise) so they move on, making it more fast-paced.

That's just what I do to keep my maps faster with the frags

^EDIT^ Yes, that's what I would do.

Spawn points:

Place enough for the number of players you think your map can hold, and then place a few more to allow servers to run your map beyond capacity. You should try to put spawn points in areas that are not easily camped but also in places that won't get the player killed the instant he appears. Try to avoid placing them in big open areas or high traffic areas. Weapons can be near spawn points depending on how you want the map to play. There's no hard rule about it or anything.

Weapon placement:

Weapon placement is an art, not a specific technique. You should have an idea of what you want your map to be and how it should play. If you want carnage, then place big weapons + ammo around but then balance that weapon by placing another big weapon + ammo in a different section of the area. An example is one of Peter Manson's maps (the one with the two sections and the jumppads separating them). In this map theres an area that is a big courtyard with two windowed rooms on the top. There's an egon in one windowed room and an RPG in the other. They face each other, so each one balances the other out since they both won't realistically be camped. You can go for a strategic approach, where ammo and weapons are spread out and allow for smart players who know the map to have the advantage. You can put the big weapons in trapped areas or out of the way spots to eliminate their impact on the game. It's pretty much up to you. However, a few things to avoid: Don't place a gun with a bunch of its secondary powerful weaponry next to each other (don't put a bunch of SMG contact grenades in one area, don't give players all three Overwatch Rifle energy balls with the gun). Don't put a bunch of health and batteries next to each other, as it really makes the game annoying. Don't put too many healthkits and batteries into the map, cause then it makes killing anyone a challenge. Make sure to put the correct amount of weaponry into the map for the number of players you have. If you expect to have a 32 player throwdown then more than one RPG may be required (think Boot Camp). The best weapon placements are tested and have a thought out purpose behind them that is constant throughout the whole map.

Flow:

The map design is an essential aspect of flow. If your map has a bunch of dead ends and poor connectivity then it doesn't matter where you put the guns. Assuming you have the map designed well then the best way I've found to encourage flow is to put the big guns in one spot and the ammo in another spot that is easily reached but forces the player to move a distance or give up a strategic position. For example I have a map where there's a rocket launcher on top of a three story building. This building overlooks much of the map and is a great vantage point for killing. However, all the ammo for it is on the ground three stories down, so if the player wants to use his rocket launcher more than the three rockets he starts with he better jump down into the fray. You could also change this around to put weapons in places where they are not very useful and the ammo in the areas where they are great. For example, you could put the RPG in a tight corridor where using it without killing yourself is nearly impossible but the rockets in the big open area.