を始(はじ)めNot only...but also..., Starting with

だけでなく and をはじめ both express non-exclusivity, but differ in nuance. だけでなく simply means 'not only (A), but also (B)', e.g. 英語だけでなく、日本語も話せる ('He can speak not only English, but also Japanese.'). In contrast, をはじめ implies that something is the first in a list of many, e.g. 日本語をはじめ、様々な外国語が話せる ('He can speak many foreign languages, starting with Japanese.').

ばかりでなく and をはじめ both introduce additional items, but their focus differs. ばかりでなく is neutral and treats both elements as equal, e.g. 彼は英語ばかりでなく日本語も話せる ('He speaks not only English but also Japanese'). をはじめ highlights the first item as the most representative, e.g. 校長先生をはじめ、先生たちが全員参加した ('Starting with the principal, all the teachers joined').

をはじめ introduces a prominent example from a group, e.g. 学生をはじめ多くの人が参加した ('Many people participated, starting with students'). に加えて simply adds another element to the first, e.g. 雨に加えて風も強い ('In addition to the rain, the wind is also strong').

はもちろん highlights an obvious example together with a more unexpected addition, e.g. 寿司はもちろん納豆も食べる ('He eats not only sushi, but also natto'). をはじめ is used to give a leading example from a larger group, e.g. 校長先生をはじめ多くの人が来た ('Many people came, starting with the principal').

を皮切りに marks the beginning of a sequence of events, e.g. 東京公演を皮切りに全国ツアーが始まった ('With the Tokyo performance as the start, their national tour began'). をはじめ lists a representative example from a group, focusing on inclusion rather than sequence, e.g. 田中先生をはじめ、皆さんに感謝している ('Beginning with Prof. Tanaka, I'm grateful to everyone').

をはじめ highlights one example among similar ones, e.g. 日本をはじめ多くの国で使われている ('It's used in many countries, starting with Japan'). に限らず expands the scope beyond the first item, e.g. 学生に限らず誰でも参加できる ('Not limited to students, anyone can participate').

をはじめ gives a representative example and implies that others follow, e.g. 東京をはじめ、全国でイベントが行われた ('The event was held across the country, starting with Tokyo'). だけでなく(て)～も lists multiple elements without suggesting one is more representative, e.g. 東京だけでなく大阪でも人気だ ('It's popular not only in Tokyo but also in Osaka').