you don't need to go online to play. At accounts page, you can create an offline account. No internet is needed for that.
Well, it being tough depends on what you set it to. The best level I've found is 80% since bots will be alert, aim sufficiently well without being snipers. Also, try adjusting the number of bots.
You need to DL the bot changer from
http://fhpubforum.warumdarum.de/index.php?topic=13624.0 and follow the instructions there. If you change them to anything above 48, switch the ratio slider to the same number i.e 48 bots, toggle slider to 48 etc. and adjuust the total bot count to 48 within the game irrespective of what number you use the app to set your bots too.
The double count can be done away with by reducing your spawn time to 0. Unlike BF42, where you had a minimum of 3 seconds, in BF2, you can have 0 seconds spawn time.
Unfortunately, we are have just 31 maps ...I know, its sad ;-) and these are from North Africa, Normandy and 3 from the mediterranean i.e Crete, Mount Olympus and Sfakia.
The development team is however working on the bulge and the eastern front, so expect at least one new theater some time this year :-)