To start rising naval buildings, one will need:
Naval Construction Yard (NConYard) or Naval Construction Ship (NCS) deploying into NConYard.
NCS can be purchased via Shipyard/Subpen.
It's faster and easier to build NConYard directly from ConYard, but:
+ NConYard is constructed and then erected 20% slower, costs $3500
+ NCS is without any negative modifiers, and costs $3500 too, but it must be bought through Shipyard/Subpen, which costs $2000 and require some other buildings first (NConYard can be built after deployment of regular land ConYard)
There will be many ways to root out a sea turtle in ASM:
1) spamming aircraft
2) spamming subs being anti-building units (yes, yes, Allies will have subs too! So there's balance)
3) spamming artillery and trying to take out the nearest vital buildings
4) spamming ships, you will be able to build Shipyard/Subpen for $2000 and place it far enough, and what's more important, w/o need of NConYard - so you can tackle the opponent without going naval at all!
There are some disadvantages of going entirely naval:
1) slower development, naval buildings take 20% time to be 'prepared' (i.e. to be placed)
2) naval buildings cost much more money; one will run out of it faster than one can think
3) also, they take a lot more space than regular land buildings
1) better Oil Derricks, providing loads of money
2) protection from short-ranged land units
3) better base defenses: they'll take much more space, but also they'll be much better armored, with greater firepower and more hps
4) NConYard can be built directly from ConYard just after its deployment, so going naval is quite easy, but requires some sacrifices
5) As with War Factories and Barracks, NConYard is counted as a factory multiplier/modifier. So +20% production time is offset by having, in fact, e.g. two ConYards (land and naval one). For each additional factory (like Barracks, Airpad, WF, ConYard) you get faster production of the specified type of units. So naval ConYard in fact gives bonus to creating buildings!
Some advantages of staying on land:
1) stronger control over the land
2) it's easier to maintain and shield land bases and ore fields
3) much more space to expand if the opponent flees or loses the land
This article doesn't contain that much info about the subject, only most essential one. ;-)