Because of how many games there are in the series, it is impossible to say that you will like all of the games based upon just the Secret subseries. This is especially true since the Secret subseries is the newest of the non gatcha games.
This generally means that you couldn't use it to evaluate properly if you would properly enjoy the older subseries, beyond part of the premise, but you would also lose some things as you went back in time too.
I'm not saying that you should start as old as possible. Just remember that the Arland subseries, the Dusk subseries and the Mysterious subseries all have different aesthetics and systems compared to the Secret subseries.

Thank you guys

I started on Firis but I would say Atelier Marie Remake is the best starting point. But you can play any Atelier because you don't have to catch up on previous stories. There are cameos though. I would say look them up and choose the one you want to play these are factors I considered.

1. Does it have a character I want to play
2. Which Atelier Main Girl I like
3. Does it have a time limit or not?
4. Do I like the battle system of that version
5. Do I like the other gameplay features of that version
6. Can I stomach the graphics

Music is another thing but not something you can gauge until you're already in it. I would usually start it out as old as possible but that's me. That's why I went with Marie Remake, now I'm on Atelier Ayesha and Shallie. I might have to have tried the Arland trilogy. I think starting from Arland is probably the most tolerable graphics wise.

All good suggestions, big thing for me to add would b e:

What sort of combat do you like, and how complex do you want it to be?

How much do you like crafting and how complex or involved do you want it to be?

Anything before Ryza (not counting side games like Nelke) are turn based combat titles, but combat can be very different between them. Ayesha's is very positional (Escha and Logy has a bit of that too), Shallie uses the Mana Khemia style build up and burst system that I personally find very satisfying, Sophie has a less interactive system where you enter an entire rounds actions and let it play out, Sophie 2 is very strategic compared to most, and Lydia & Suelle is incredibly buff and debuff heavy. Most of them have some way to trigger actions of your other teammates to set up combos, some require a little bit of timing while others don't.