I just released a mod for getting seeds from existing tomatoes, but you'll need an admin to create some if there's no tomatoes left. Either way, I recommend getting the mod to make tomatoes sustainable once you have some seeds:
http://ecoforum.strangeloopgames.com/topic/3571/tomato-seed-recipe-crop-viability-mod
I've created a crop viability mod for my server. Initially it will just contain a couple of things to make otherwise unsustainable corps usable, but my mid-term plan is to make fertiliser useful if impending patches don't address the issues with it. It's really affecting my ability to farm...
Right now the only content is a tomato seed recipe (turn tomatoes in to tomato seeds, like some other crops), because tomatoes are totally unsustainable crops at the moment.
You can pick it up here
Just extract that zip in to /YOURSERVER/mods/
If you have any requests for content let me know.
Yes. The world generation and game rules are in the hands of the admin. The main 'difficulty' factor is collaboration modifiers, in a 1-4 person game you will have 'very low' collaboration generally and in a high person server you'd have 'very high' collaboration. This basically limits skill rates and alters the costs of specialising in multiple fields. This is generally a better way to represent larger and smaller communities than simply giving everyone 'more stuff'.