[Slick]

Here's my advice on Weapon Platforms: Build them only when you can't build a ship to do the same job. Ships and fleets have many more advantages. WP's are good for using up excess income if you have all your Spaceyards working already; but this means you really should be building more spaceyards. If you are using WP's, this means you are fighting the war in your systems - this is bad - you should try to fight the war in the other guy's systems. They may make you feel like you have a security blanket, but a decent fleet can normally easily glass or capture even a well defended planet.

They can be used as an emergency means during early contact, or to establish an outpost where the enemy doesn't have a fleet around. But SE4 is rightfully biased in favor of ships. If planets could overcome fleets, games would end in gridlock. Planets have disadvantages in defense (-200%!!) and in cargo capacity. They have advantages in range and damage multipliers for WP mounts. These can be used temporarily as a stop-gap measure (as can other units like mines, fighters and drones (which are not very good)), but if you invest in WP's at the expense of spaceyards and ships, you are asking to have the war fought in your systems while the enemy flourishes and continues to expand.

I recommend reading section 17 of the Newbie FAQ, written almost 100% by Stone Mill (former King of the Hill) and respected PBW player. Specifically 17.3.7 "Economic Harmony" really opened my eyes after I started practicing these techniques. Previous to this, I had been building too few spaceyards on planets, using too many WP's and not developing my empires as efficiently as I could have.

edit: As far as what kind of WP's to build, I recommend building the largest you can (to take advantage of the range and damage bonuses from the better mounts and that they have more hitpoints before being destroyed) and designing them to have some shielding or armor so you can minimize the micromanagement of them.

Slick.