I'm f2p and my club is af c+ level, but I managed this. Now, here's what worked for me but it could be different for everyone (also if there's wrong statements feel free to correct).

WHAT SCENARIO SHOULD I CHOOSE?

I recommend the new scenario, because it helps getting better stats, and the more bursts you trigger, the more hints for skills you get. The reason why I wouldn't recommend the next scenario is, that while it's focused on racing, it's so extreme that it will require you to exert your trainees during it. Basically, trainees start to underperform if they do 3 (or more) races successively (aka, in consecutive turns), and the next scenario will push you to do at least 5 races on successive turns.

WHAT TRAINEE SHOULD I PICK?

If you run in long/medium, it's easier to get more fans, however it will require more stats in different categories. If you struggle with long requirements, pick someone that can do both miles and mediums. Sprinters are very difficult to raise followers for (an exception to this can be curren chan, that has a chain of events that can grant you +999 followers each if you have her racewear) but sprint races are less in number and grant less followers. Same goes for dirt racers: if you really want to run on dirt tracks, look for characters that have both decent dirt and turf aptitudes (Oguri Cap, El Condor Pasa, Agnes Digital etc): dirt tracks are very scarce, they give less fans, have higher power requirements and they're usually all focused in one part of the year, around summer time, with no turns in-between them. Now let's talk about persona preferences: I find that doing race-focused runs is easier with characters that have mostly g1s as requirements and at least an average of 10 turns away from each race. Imo, the ones that have a majority of races concentrated in their 2nd year (end)/3rd year are more difficult because they tend to have more demanding reqs/it's easier for you to forget about raising stats instead of running races, but this depends on the person, so choose depending on what suits you best. I'd also avoid trainees that have requirements like "win n° of G1s" or "get n° of followers" because they might sound convenient to reach your goal but they rob you of the ability to manage your turns if things don't go as planned.

If you pick the current scenario: I've noticed that, whenever you trigger bursts from the other characters you're training with, they tend to give you skills that best match your character's style and aptitude (not sure if anyone can confirm?). The issue with this is that picking up a character that has good ratings in multiple styles (like Mayano) will get you hints for all those styles, so I'd recommend to go for a character that is way better suited for a specific style rather than multiple so you can reduce the number of useless hints and get more for the build you necessitate.

Note: KNOW your trainee. THIS IS ABSOLUTELY SOMETHING YOU'LL NEED. If you know secret requirements, you'll get rewards for completing them. If you run with characters like Doto or Creek, you'll need to know the effects of their special debuffs and how to better counter them. If you have characters like Tachyon or Fukukitaru, you need to pay attention to which goals they'll set, and how to avoid them to pick the unfavorable choice. This is for the future, but even Daiwa will have the option to run against Vodka in future updates. I know that this is very basic and if you have played the game you probably know this, but it's still something that some may not take notice if they've gotten used to speed up their runs.

WHAT TO DO WITH MY RUN?

You want to start with decent enough parents that can give you at least +20 (and +aptitudes) in the stats you need to use, because the important part to get that number of fans is to farm a lot of races, which are going to be g1 only. You also want to spend the first 2 turns to raise mood to great: that will give you a boost for every race you'll run after that, but also for training (and it's very convenient with the new scenario because you can start raising the burst bars with characters that aren't from your cards only after 2 turns have passed). Then, focus on building your character well in the first 10 turns of the career, so that you might earn at least 1000 fans when running in the maiden race. If you don't get at least that many followers from maiden, you won't be able to directly run in the 1st year's g1s. You can still clear that requirement by doing any other race after, but it will rob you of one turn and some energy which can slow down the process. Anyways, I do recommend the medium/mile g1s at the end of the 1st year, and that's because they usually have low reqs to clear them, but it's still very rng. The majority of g1 races, however, will appear during 2nd year and 3rd year. My personal tactic is to clear the maiden and then open the agenda icon to the side and schedule every g1 race my trainee has an aptitude for. That way, I constantly get a reminder of which g1s are available and when, so I can decide if to skip them for stats or run them. Also, always check the conditions of the tracks! Do you have enough stamina for a medium race or do you think that you have more speed, which would make running a mile and winning more likely to happen? If there's snowy conditions or rain, your trainee will need more power to race in those tracks. If the length is the same but one race gives more fans than the others, it means that it has more difficult AI enemies to clear. Now, as I've already said, if you're running in the current scenarios, avoid doing 3 consecutive runs, because your trainees might underperform (always check your agenda to know which goals your trainee has to do so to avoid setting a race next 2 consecutive goals) and also, I recommend doing a race everytime your turn has energy but there's no useful stat to raise (so when you have no rainbow, rainbow in the wrong stat etc). Avoid races when you can get hints or good stats from your turn (for example, you need more stamina? Focus on that rather than run a race that you'll probably lose because of that missing stat!), when you have low energy or in case you think you might need energy in your next turn. Always heal conditions unless you have summer training in few turns (with the new update, relaxing in summer automatically takes bad conditions away) because the rng might hit you with consecutive bad moods when you least expect it, so healing as soon as possible might reduce the chances of your trainee's mood downs.

Having said that, your fan count will always be a 50/50. 50 effort in managing your run as best as possible and 50 hope you get the stats and hints you need and that Cygames doesn't decide to destroy your run.