I think there are a lot of misconceptions about the best way to train when you first start off in this game. Let me offer you a different perspective from the post above me.
First off, if you are paying 13k salary a week for a trainer, you are paying about 130k+ more over a season than you would pay for the default trainer. This means in order to be worth it, the trainer would have to be adding about 130k in market value to your players more than the default trainer would.
According to the BB croudsourcing training project, the difference between a level 4 and level 6 trainer is only around 5%. I think it stands to reason then that the difference between level 1 and level 4 is less than 15% (anecdotally I couldn't tell the difference). I think it is quite unlikely that 15% faster training for a player in a V league is going to be worth 130k.
My advice: stick to the default trainer until you are confident you have a training plan where 10-15% faster training is going to add at least 130k extra value to your trainees.