Do This First, Then Decide
上で marks a first step taken deliberately so that a second one can follow properly.
- 資料を読んだ**上で**ご返事します。(I'll reply after reading the materials.)
Both actions must be intentional, and the second usually involves a decision, a judgement or a formal response.
Against てから
Both mean "after", and the difference is purpose:
| Pattern | Sense |
|---|---|
| てから | simple sequence — A, then B |
| 上で | A is the basis on which B is decided |
朝起きてから顔を洗う is fine. ×起きた上で顔を洗う is not — washing your face is not a decision made on the basis of waking up.
The Second Sense — "In the Course Of"
With a noun, 上で can mean "in doing", naming a domain rather than a sequence:
- 生活する**上で**必要なもの(things necessary in daily life)
Here it attaches to the dictionary form, not the た form. The tense tells you which sense is meant.
Not 以上は
Same kanji, different pattern. 以上は draws an obligation from a fact; 上で marks a sequence or a domain.