Also, I tend to disagree with the notion that fleets are the key to victory. *Some* naval presence is crucial to everyone, even Austria, but armies are far more decisive - while there aren't many landlocked SCs, there are plenty of crucial landlocked spaces that will decide the ability of a country to convert a strong naval presence to an outright win. A general rule of thumb I like is that for each "sector" of potential naval influence - Turkey/Eastern Med, Italy/Austria/Central Med, France/Western Med+MAO, England, Scandinavia - there's really no use for more than 4 fleets at a time:
Turkey: BLA, EMS, AES, ION
Italy: ADS, ION, TYS, Tun
France: GoL, WMS, MAO, ECH
England: ECH, NTH, IRI/NAO*, NWS
Southern Scandinavia: HEL, Den, BAL, GoB
Northern Scandinavia: SKA, Nwy, BAR, GoB
*: Five fleets is more useful than 4 here, of course, but as IRI and NAO serve very similar purposes (backdooring into Lvp) you can suffice with 1 and do fine.
Scandinavia I had to split into two. You'll probably want 5-6 fleets concentrating on Scandinavia if you have to take the whole thing at once (say, lategame Russia/Germany owns it and you're England about to stab that long-time ally), but you can get by with 4 if you divide and conquer; hence the split into Southern (which looks more at Germany honestly) and Northern (Scandinavia proper + St. Petersburg).
At most you'll only want to add more than 4 fleets in cases where:
(a) you're engaged in a 2-front naval war (Italy, fat off of dominating Austria, moves against Turkey only to find France gearing up to hit him in the back), or
(b) you're England (rarely Turkey) and find convoy chains compelling.