I don't know. The more I read up, the more uncertain I become. One thing is for sure, the choices I will make for parts will have great impacts on the bikes handling and performance. And there sure is a lot more to building an e-bike then I thought when I first came onto this forum. Really that just makes it a bigger challenge to do both the proper research ahead of time and to ensure the build will start out with the best possible parts and design to meet my budget and criteria.
EXCELLENT!
If you want something to ride the first time out within the next year you will need to understand all the components and decide which one are DIY candidates. It is virtually impossible for a single person to singlehandedly custom design and fabricate all components a solid reliable high performing ebike.
Weight - cost - performance. The golden triangle of ebike parts selection.
Weight - This is the easiest design goal to define as all you need is a simple scale. All components can be lightened up. Main aspects are weakening and cost. Light and strong costs $$
Cost - This is more involved as there are multiple variables. Simplest is $$ changing hands. Time and energy are forms of cost as well. For each make vs buy decision you are settings values in the cost calculation. In DIY cases, rarely does one slide through without some redo or added costs for unforeseen events.
Performance - increase power to the wheel. This is the most difficult as there are so many variables in an ebike. The battery pack is a simple object yet has quite a few considerations. Even a buy decision is really critical to get just right as the cost is so high. The more tidy the pack is the less adaptable it is. Alternatively, a bunch of cells and small packs taped together offers more flexibility to reconfigure the pack when you likely want to add volts to what you figured would be enough or more capacity due to ride time.
Even the lonely charger gets so little attention yet charging performance can be a very important criteria for some riders. Most newcomers to battery technology are not even aware of cell management and ensuring all batteries remain balanced and such.
Then there is the controller. Not properly sized and properly managed by yet other components such as a cycle analyst, you will read about the brief cloud of smoke when you inadvertently run the bike too hard.
The brain such as a cycle analyst serve as the eyes and ears on what is going on with the power drive system. It also can control the throttle to avoid blowing things up and allowing things to have a decent life.
Drive systems - hub or mid drive or? So many options and the integration with existing mechanical drive system. Proven designs in high power configurations run left side drive to keep power out of the bike drive system. Bike drive systems are not designed to handle power dished out by many ebike systems. Even if you stay under say 1500 watts (constant running load) you have regular gear configs as well as IGH options.
Motor options - You will find quite a few major categories and then when you dig in you will find quite a few different offerings and options in each.
Wires galore and a lot of reading on harness systems and routing and gauge and connectors.
Then you have the entire topic of frames, wheels, tires, rims, etc. So so many ways to here.
The list goes on and every item on the list has its own sphere of technology, methods, builds, costs, performance, design parameters etc. Attempting DIY on every item requires a solid understanding of all the factors relevant to that component.
I'm glad to hear you feel your eyes and ears opening more and receiving a flood of information. Like I mentioned before I am about 5 months into this journey and feel like I can at least ask an informed question in most areas. All this shows is I have a basic understand of the principles at play and can just commence serious evaluation, design, and selection of all the key components. I try not to get diverted into subjects such as lighting and various methods for connecting them or options for power system cut off switching, etc.
In the end, the only practical and reasonable approach is to understand how and what makes up a solid running bike then decide what makes most sense to you to DIY. Select and buy what you've chosen to purchase. For each DIY components plan to spend a lot of time developing a deeper knowledge base so you can design and build something solid and reliable.
From my vantage point something like a custom carbon frame is hardly worth considering. Going back to weight-cost-performance. It is quite easy to toss this off the DIY list. Cost is quite high. Once built alterations are quite difficult. Is a really stiff frame something you even want. Maybe a softer more flexing frame is better suited to absorb some of the road. The few pounds difference may make a big difference in a road race bike but on bike pushing near 100 pounds, you can get those pounds elsewhere for pennies on the dollar.
Glad you are on board and learning a lot and keeping the credit cards locked up for awhile. It will pay off big time once you do learn sufficiently to design a solid running bike. It takes time, more than you think, especially since many components are linked and intefaced to others. So a change in one impacts one or more of the other ones, somethings a simple ripple but sometimes a major resign and rethink.
Keep it fun and a hobby even if it were being designed to be your primary commuting vehicle.