Let's begin by defining some static values.
The table below shows the cost of making a tiered Classification 4 equipment both from Tier 0 and from the previous tier. These values come from assuming a supplementary Classification 4 equipment of 5kk + the cost of Convergence Fusion (the most common method for tiering up very expensive/bis equipment).

The table below shows the values of all effects.

Below is the table with the increase for all tiers in all effects:

All in all, we have that:
- Upgrading Onslaught from T1 to T2 costs 175,000,000 and gives a 0.55% increase.
- Upgrading Ruse from T1 to T2 costs 175,000,000 and gives a 0.53% increase.
- Upgrading Momentum from T1 to T2 costs 175,000,000 and gives 2.05% increase.
- Upgrading Transcendence from T1 to T2 costs 175,000,000 and gives 0.14% increase.
Given the above, we can say that, if you have a T1 set, 0.55% more in Onslaught is worth 175,000,000 gold.
In this context, upgrading the boots from T0 to T1 would yield the following:
- 0.0125% more in Onslaught, worth 3,977,272.72 gold.
- 0.0125% more Ruse, worth 4,127,358.49 gold.
- 0.05% more Momentum, worth 4,268,292.68 gold.
- 0.00325% more Transcendence, worth 4,062,500 gold.
Therefore, the entire gold value of adding a T1 boots on top of a T1 set is: 3,977,272.72 + 4,127,358.49 + 4,268,292.68 + 4,062,500 = 16,435,423.89.
Below is the table for how much is the gold value of upgrading boots on top of each tiered set, truncating decimals:

The asterisk marks where the gold value of tiering up the boots is higher than the cost of doing so.
The optimal plan, therefore, is:
1. Upgrade set T0->T1->T2
2. Upgrade boots T0->T1
3. Upgrade set T2->T3
4. Upgrade boots T1->T2
5. Upgrade set T3->T4
6. Upgrade boots T2->T3->T4
7. Upgrade set T4->T5
8. Upgrade boots T4->T5
9. Upgrade set T5->T6
10. Upgrade boots T5->T6->T7
11. Upgrade set T6->T7
12. Upgrade boots T7->T8
13. Upgrade set T7->T8
14. Upgrade boots T8->T9
15. Upgrade set T8->T9
16. Upgrade boots T9->T10
17. Upgrade set T9->T10