Clara - are you me? Seriously, two years ago, I was looking at growing exactly what you are now.
Strawberries - after doing some research, I realised it is better to buy good quality plants rather than attempting seeds. I got mine online from greenfingers.com and planted them in early May. They have done very well and I got a good crop both years they've been in. This year I also was able to propogate more and now have some in pots which I plan to give away if they make it through the winter.
Tomatoes - I agree that rather buy plants. Again, wait perhaps until April otherwise it will be too cold. I planted mine in growbags but think that two per bag in future is the most I'd go for. My father recommends planting one plant in a large pot rather than a grow bag. They DO need feeding however and once it gets warm and hot they need to be watered pretty much daily otherwise they don't do so well. I also planted marigolds near mine in an attempt to protect them. I don't know if it worked or if it's just a coincidence but I didn't get any bugs.
Herbs I've been growing for years. Categorically, I have better luck when I buy quality plants - go to a proper garden centre rather than the supermarket or even B&Q. Rosemary is very easy and hardy - just pop it in a pot and away you go. Thyme likes it fairly dry so plant it in a dry spot or use a pot that is well drained. Also, I recommend getting a few plants as it doesn't take much cooking to very quickly decimate your thyme. I grow mine in one of those ceramic planters will multiple spots for herbs - very mediterranean and I find it's a good way to get the thyme to stay thick. Basil is an annual so it will die every year. That's normal. They key to keeping it alive during the season is to water it regularly. It needs a small amount of water daily. Coriander I'm afraid I've had no luck with, but then, I've only ever tried to plant my supermarket coriander. This year I'll buy some properly.
Parsley and mint are great to have in the garden too. But plant mint in pots as it will spread otherwise. It also needs lots of water. Parsley also needs a generous amount as it only takes one meal to find yourself all out of parsley.
Hope this helps. Hope it's not too long.
Oh, and I agree re RHS website.