It warms my heart to see this game getting love from people. I love this game, but I have to admit, you really need a guide for this game.
A few tips from myself.
*GET THE SHOP OPEN ASAP. So you can buy 2 of the most vital items in game, auto pilot and portable potty. Fast travel and every Place toilet is a god sent. And if digimon doesnt wanna eat the toilet, just scold him. Most of the shop owners can be gotten on the way to Gear Savanna. Get Patamon, Biyomon & Unimon.
*For "easy" champion aka no Numemon, try 1000 HP and MP and 100 for rest. This is almost minimum requirement for all champions. Honestly, weight doesnt seem as important for champions, so no need to care for that. Only warning is that these stats dont work for Elecmon. You need higher stats and more specific requirement fillings. So Elecmon is easiest way to get Numemon if needed.
*For "easy" ultimate try 3000 for HP and MP and 300 for rest. Usually this is good minimum amount of stats required. Now of course there are quite some ultimates that need more and different stats and care mistakes and weight requirements, but usually this is good starting point. Also earliest ultimate is possible is usually after 6 days. So you can train all stats entirely for one day to get optimal results. This might be hard in beginning of game, since you may have limited food resources but this is optimal for late game.
*If you dont have emulator, screw Bonus Try's. Yes they can help, but they have way too much risk to be useful.
*This game will probably resort you to restart PS1 if you want best results. It is unfortunate, but nothing too major. This a case mainly for all techniques, as you can get techniques if you train brains and the infamous Monochromon minigame.