Well done! You are on the way!
So now you get down to the trickier bit... Growing in soil is great for the new grower - it's much easier initially and produces great quality.
However....
It may take you a while to find the right kind of mix. It always helped me to try and remember what I am trying to achieve rather than treat each problem separately.
So, what you want is a substrate which will hold the plant up, while providing the correct amount of nutrients and aeration.
1) Holding the plant up
It may seem obvious but this is one of your main concerns. As your plant matures (and grows more tomatoes) it will become top heavy, you need a decent foundation to keep it up. This means a solid _base_ i.e. not too much perlite and a decent pot.
2) Nutrients
This is what most people get hung up on and where they make most mistakes.
Remember, you want to keep your plants fed for about 2 months, after that (depending on how long the strain needs to flower), you should be leeching the soil so all those elements don't end up in the final product. When you pull it out of the ground there should be no neuts left.
The balance of neuts and ph levels I honestly forget, but they are handily written on the back of your soil packet

There are plenty of places on the web to find the optimal levels. To modify what you have to the optimal - use some vermiculite, ph balancer or top up with some off the shelf neuts. Vermiculite is basically a substrate which comes with no nutrients in it.
The key to all this is: if you make a change to what the plants are fed, it will take them about a week to show the result so, as always, be patient
3) Aeration
Roots need air - if your mix is too stodgy it will have no air in it - that's what the perlite is for.
Remember to prevent the roots from growing out of the bottom of the pot by lining with a mat and some (washed!) gravel)
Somebody help me remember what that stuff in you can buy in a chemist that you add to the water to help aerate it.... H2O3 or something?
So, that's a quick brain dump for ya, hope it helps.
The Webguy