I totally agree with the above comment by
@WorstDecorator if your aim is levels and an overall better fishing experience. If you're really struggling to catch catfish at level 4, level 5 probably won't make that massive a difference, and you'll want to follow that advice, you'll inevitably get better at fishing for later runs, too. That being said, it looks like you're intending for the level 5 to be more of a means to an end, and that end being money in the very first few days, rather than a continued fishing journey.
Accounting for that, you absolutely want to do as setrux has already advised and invest early in a fiberglass rod, but would try to do so even earlier. While fishing at the beach is slightly worse, you more than make up for it by being able to sell directly to Willy on day 2, and don't waste time running to and fro. Let yourself to pass out every early night, you should try to keep your funds low, and since you're levelling up fishing a lot, you won't suffer from any energy loss. If you're fast enough, you should be able to nab the fiberglass rod effectively immediately as soon as you level up on day 2, though it probably depends on how well you can perfect catch at early levels (you'll want ~1400-1500g from fishing + whatever foraging you did on day 1 alongside your 500 starting cash to afford it and some bait).
Secondarily, you'll ideally want some trout soup for the first catches on day 3, but it can mean buying it in the morning of day 3 if you bought the fiberglass rod day 2, as it's definitely a tight squeeze to afford that. The cooldown on the buff should be enough to last you until a level up, and ideally a bit longer, which may allow you to catch a few catfish.
If you notice you still aren't able to catch that many catfish (try for at least a catchrate of >40-50%, of you're really just wasting your time), eel are also decent money in the ocean, and have a pretty good window of the afternoon and all of the night.