완료형 and 가정법(subjunctive/conditional) can be difficult, but you seem to have a good basis for understanding them.
완료형 is expressed through the past tense in Korean. There is no separate perfect tense form.
One difficulty is that it changes with the verb usage, i.e. whether it's in predicative or adjectivized form.
* Predicate form example:
- A: 영철 씨가 안 보이네요 (I don't see 영철). B: 영철 씨 휴가 갔어요 (He's gone on vacation - present perfect).
* Adjective form example: (-(으)ㄴ represents 완료형, which may be the past or present perfect)
- 휴가(를) 간 사람 = the one who has gone on vacation.
- 내가 끝낸 프로젝트 = the project I have finished.
For adjective forms, perfect continuous is expressed with 던, and past perfect by adding -(어)ㅆ to 던. These two can combine to create more specific connotations such as "used to" and "would" denoting a past habit.
- 내가 하던 일 = 1) the work I was/have been doing, 2) the work I used to do. The exact meaning depends on the context.
- 내가 했던 일 = the work I used to do.
NOTE: 하던 (present form + 던) indicates what has been going on for a while (perhaps until recently) and which can possibly resume, while 했던(past form + 던) indicates it happened in the further past and there's no possibility of resuming (similar to, but not exactly the same, as past perfect in English).
When it comes to conditionals/subjunctives, the subjunctive sub-clause usually has the verb ending -면 which represents "if". The main clause is expressed with the 겠 or -ㄹ 것이다/터이다 form (and its variations like 건데, 텐데, etc).
* Second conditional example (the sub-clause takes the present or perfect tense; main clause takes 겠다/-ㄹ 것이다/터이다).
- What would you do if you were in my shoes? = (만약) 네가 내 입장이라면 어떻게 하겠니 / 할 것이니/거니?
("in X's shoes" is "X의 입장이다" or "X의 처지가 되다". 신발 안에 있다 makes no sense in Korean)
Third conditional examples (the sub-clause takes past or past perfect tense; main clause takes ㅆ겠다/-ㅆ을 것이다/터이다).
- 너무 바쁘지 않았으면 네게 전화를 했을 텐데 = If I hadn't been so busy, I would have called you.
(Your 바쁘지 않았더라도 means "(even) if I hadn't been busy, (I would still ...)", an entirely different thing)


