IMac for music production

What's going on everyone. I've always used pc but I'm really liking how these iMacs look and really want to get into logic. I've been looking online trying to figure out how I should get this configured so this could run flawless for me.

I will definitely go with an i7. I seen that upgrading the ram myself would come out a lot cheaper so I was wondering if anyone had any recommendation what brand I should go with. Use a tom of kontakt and other vsts so I'm thinking 32 gigs of ram should be best.

Are the hard drives able to upgrade easily or should I just go with the ssd upgrade from the Apple site?

Lastly, for external hdds would any of them be good to just connect up and use? I've been using the wd passports for other things but nothing yet as for putting music files and libraries. I've only used internal hdds on my pc.

Hope I'm clear on what I wrote down and hope to get some advice. I appreciate it. Thank you.