1. too much if have to write step by step on this page

I assumed a Mining Rig if anyone suggesting ASIC it's more variation, so, @OP has many choices

2. Purchasing hardware like Motherboard, PSU, SSD, USB Riser, Processor, RAM, GPUs

Note:
-usually, miners a purchasing a motherboard has a lot of PCIe slots is minimal 6x PCIe.
-PSU adjust with how many GPUs
-USB riser Ver008c
-Processor Celeron is enough for Intel Chipset
-RAM 4GB is enough but 4++ is better.
- AMD cards (Rx series, Vega) NVIDIA (10xxx Series)

3. Reading about coins and find profitable coins.

Note:
coins(algorithm) adjust with GPU type, used a precise algorithm (GPU type).