You forgot to mention your actual location, as your local prices may vary dependant on your location 😁
As of hardware: definitely go for AMD 5xxx 7xxx series, anything over 6 cores would do the trick, the higher the max GHz, the better, guess last Ryzen 5 (6/7 gen) go up to 5Ghz and can firmly keep em turboing. and would strongly suggest going at least 3060 for gpu, 3070/4070 would be preferable. A decent SSD is a must and yeah, at least 16 GB RAM, no 8GBs would save you today, but 32 would.
Something like Lenovo LOQ 15APH8 would probably do the trick technical wise, but have no idea what would be the price for one at your local traders. BTW im not a fan of Lenovo, no rocks please, just an example of config.
And yes, you can definitely add more RAM later on, but you can't swap a GPU out.