Hmm...
Every player plays as feel to play. There is no right or wrong just entertainment. It is just a game.
Now, looking about the way to progress, it is all depending on your amount of farming you do per day/week.
As basic...
1-The BASE HQ should be level up until can get the 4 gold mines and no more.
2- The gold mines can be worked to reach L20 in order can get max gold grant per day that it is 100k.
3- The BASE Factories-- Everyone will tell a different comment. Now, I will say keep the factories in L2. There is no need beyond level 2 if you are not a heavy grinder. Factories at L15 are for players that grind a lot. Crafting power kits as example in L15, it does cost a lot to recover back grinding with just 400 power kits to get them in full in 1 day and 5 hours and will cost 2.3 million to craft them as basic.
Even for me at full grind in my best time 24/7 not missing hours, it does drain a lot of gold resources and need to be balanced with mixed boxes collected during farming.
Do not forget that will require to use gold to max a part and crafting it is an extra expense.
You need to calculate how much gold do you farm per day/week.
Normally "not all of them", it will cost 1 million to max one part from MYTH LEVEL 1 to MYTH LEVEL 50.
That it is not including how much cost from L1-L40 as legend and epic if was an epic item.
For lower grinders, factories at L15 are a waste of gold or can be ok for just one and the rest to be kept on L2.