Miracle-Gro

You get a much better germination rate using a branded seed compost as the structure is formulated for optimum seed growth and it is also sterile so should minimise the risk of fungal outbreaks.

Yes, this is crucial. If the feed to water ratio is too strong the feed will burn the plants roots which means it won't be able to take up water and will inevitably die.

General purpose fertiliser is better than nothing but a dedicated fertiliser has been tested over several years and is proven to give you the very best results from your plants.

If you are going to the trouble of growing plants, whether fruit and vegetables or flowers it makes sense to have them achieve their maximum potential.