Learn Hardcore Chinese: zhèyàng zuòqǐlái gèng róngyì.

mark the start of an action (他笑起来了 = He started laughing),
indicate upward/collecting movement (把东西收起来 = put things away),
give an evaluative/experiential sense: “when you do it, it feels/seems ….”
In 这样做起来更容易, it’s the third use: “When done this way, doing it feels easier / turns out easier.”

Can I just say 这样做更容易? What’s the nuance difference without 起来?

Yes, 这样做更容易 is correct.

With 起来: emphasizes the experience of carrying it out (“once you actually do it this way, it proves easier”).
Without 起来: a straightforward statement about ease, with less “experiential” flavor.

Who is the subject here? Is something missing?

Chinese often omits a subject when it’s general/obvious. Here the topic is the method: “Doing it this way is easier.” You can add a subject or topic:

Do I need 地 after 这样 (like 这样地) to modify the verb?

No. 这样 already functions adverbially as “in this way/like this.” 这样地 is unnecessary and sounds odd here.

What’s the difference between and ?