Copy GameData folder into your NFS Porsche Unleashed installation folder and replace the modified "...\Need for Speed Porsche Unleashed\GameData\Simulation\AI\prsonal.csv" file with the one provided here. Maybe create a backup beforehand of the file to revert if needed, or try to modify it yourself. Just replace all settings with "Low" to make the game a bit easier. Or turn everything into "Extreme" to make it a lot harder.

You still need to buy the best car depending on the era, upgrade it with the best parts and do proper tuning. See screenshots in base folder for examples or look for the "Need for Speed: Porsche Unleashed Unofficial Strategy Guide and FAQ by Kasey Chang" online to get a better understanding.

The recommended options here are everything according to screenshot, except for some cars, especially the 911's you might have to use 40 instead of 45 as the front wheel pressure to get it more stable. Also most cars are better with 81/27, some are better with 99/33 downforce ratio configured. On Alps track consider using rain tires to reduce slipping in the snow.

To make money you normally have to win races, though most prices don't even break even with the repair costs depending on the cars.
Alternatively buy used cars, repair them and resell them immediately for profit.
Just buy the most expensive ones you can afford, as many as you can afford, but keep some money for repairs.
Put the highest possible price to auction (e.g. 9999999), you will still get a good offer once you exit the garage.
Just repeat until you have enough money to finish the career. If you have some money buffer, buy multiple of the racing cars of the first and second era. Then sell those in the third era. Especially the "Moby Dick" has the highest profit margin in the final era.
I guess the game wants to advertise that porsches are a good investment, that's why you can only make enough money by taking good care of the cars.

Some races will still be hard, especially some factory driver missions. But the game is still a lot of fun and teaches very nicely the fundamentals of tuning with its exaggerated under/oversteer physics model.