By the way, being a slow trainer does not mean that your player will be inferior in terms of performance on the pitch. He might still produce good performances for 1-2 seasons. My first good performing ST was a slow trainer. He returned a decent amount of good performances, including a lot of goals for the market value and tokens he costed, but definitely needed to be sold after 2 seasons. So, you can keep your ST/AML for another season.
The advantage of slow trainers is that they cost relatively less in terms of virtual money (market value) as compared to fast trainers which can easily put your finances in red if you bid for few in the same session and win all of them. Given the fact that you are new, it might be best for you to get a mixture of 'nordgens', mainly slow trainers but having high quality (95-99%, if bought in week 1 will, by week 3, be displayed as 6 stars), and a few 5 star fast trainers in which you can 'invest' your extra green packs and personalise them as you want as long as the personalisation fits to the qualities they have (attributes and positions). You can also get a few 'nordgens', fast and slow trainers, with the right special ability already assigned.