You only need two [Force00x] listings. One for the good guys & on for the bad. Make [Force001] USN and [Force002] the IJN, or whatever your primary forces will be for each side. All other U.N. nations will be 'under the command' of [Force001] (i.e. Australia, RoyalNavy, USMC ..) or of [Force002] (Japanese Empire, etc..). These nations will then be listed in the CAMP_DATA.ini's Nation= section.
Next, make sure that [Force001] & [Force002] and all other Nation= belligerents are listed in your Nations.ini.
Having the Solomons folder with the Solomons.ini pointing to the Solomons_DATA.ini is all correct. The campaign folder must be named CAMPAIGNS, though.
The Solomons.ini should look something like this -
[CampaignData]
CampaignName=Solomons
DataFile=Solomons_data.ini
CampaignMap=Solomon-V3
NavalCampaign=TRUE <<<<<<< If using SF2NA
Service001=USN <<<<<< These will be the nations listed in your SOLOMONS_Data.ini that you want to make flyable by the player. If you don't want to fly for the Jap's, then there's no need to list them here. This is the 'callout' for the lisitngs below, which make up the menu screen listings when selecting a unit for your campaign.
Service002=USMC
Service003=
Service004=
Service005=
Force001=US Navy
Force002=Imperial Japanese Navy
[uSMCUnit001]
Squadron=VMF223
ForceID=1
UnitID=1
StartDate=09/01/1942
DescFile=
StartText=Solomonstart.txt
AircraftType=F4F-4
[uSNUnit001]
Squadron=VS-8
ForceID=1
UnitID=2 <<<<<<<<<<<<<<<<<< this # - [AirUnit002] from the SOLOMONS_DATA.ini must be listed as 2 here
StartDate=09/01/1942
DescFile=
StartText=Solomonstart.txt
AircraftType=SBD-3
[uSNUnit002]
Squadron=VF6
ForceID=1
UnitID=3 <<<<<<<<<<<<<<<<<< this # - [AirUnit003] from the SOLOMONS_DATA.ini must be listed as 3 here
StartDate=09/01/1942
DescFile=
StartText=Solomonstart.txt
AircraftType=F4F-4
The [AirUnit00x] from the SOLOMONS_DATA.ini is the UnitID= for the SOLOMONS.ini.