Hcg levels and implanration time question

Alright ladies, i have aequestions that i really have no idea about. I have had 3 pregnancies this far. First 2 i have 2 healthy babies. 3 was mc last month. The first i didnt find out about until 7 weeks, just never tested until then. The other 2 i found out at right around 4 weeks. Faint positives but they were there.

My 1st question is this:

Can HCG levels be high in the beginning for some pregnancies, and for others be lower and take longer to build? Like one pregnancy at 4 weeks they are 50, another they are only 15?

My 2nd quesition is this:

Does it take roughly the same amount of time to implant for each pregnancy a woman has? 12 days last pregnancy, could it be later next time, or would it still be around 12 dpo?

Sorry, i am just wondering these things. Thanks for any help you can shine. Baby dust to everyone.