There is a bit to unpack here. I am going to lead with a bit of advice/explanation of my recommendations. A hard lesson that many of us learn is the concept of buy once, cry once. So many people enter into this hoping to build a bike for as cheaply as possible, and end up regretting it down the road as they then have to spend twice as much money doing things over again. Sometimes it's worth spending the extra little bit of money up front so you don't have to spend a lot more money later.
With that out of the way... right off the bat I want to warn you about your choice in bike. Those Huffy Nel Lusso frames are one of the least safe bikes to do a build with. They have the absolute thinnest tubing possible and tend to have poor welds that crack easily. You have been warned. I won't say anything more about it after this, just know that most of the people here will agree with that assessment. You are better off with a Kent Bayside (
slightly better), or a Hyper Cruiser (best) to build a motorized bike with if you need to stay to a budget.
As or mounting the disc brakes. The rear can be done with no welder. Both Damien here, and
@Gordy made brackets out of aluminum without any sort of high tech machining or welding. As long as you have a drill and a grinder with a cutting wheel or some form of cutting tool capable of cutting and shaping aluminum you can make a rear bracket.
The front brake Adel clamp thing is fairly straight forward. You mainly need to know what size the fork tubes are that you need to mount the clamp to. The clamps themselves are easy to find online or even at some hardware stores. The other option would be to simply buy a fork set with a built in caliper mount. There are a thousand options out there and several price ranges to work in. Again, I am just recommending the "Buy once, cry once" approach.
