I've welded using gas and arc and arc is a LOT easier to learn but the easiest and least expensive method which will produce the best job is to cut all the pieces to the correct length and take them to a professional welder with all the joints well marked. I have all the confidence in the world I can weld a bicycle frame (steel) but simply don't have enough call to own a welder, especially when there are a dozen professionals within ten miles of where I live.
Cutting is easy and inexpensive. A used chop saw (miter saw) and a metal cutting blade will cut most anything and cut it at an angle. A new grinder is inexpensive and Harbor Freight ships anywhere and is getting more and more retail outlets. They, for the most part, are Chinese tools but for the homeowner and light tradesman do a good job for the money. They also have inexpensive welders if you go that route.
Electric drills are a different animal. You definitely get what you pay for but Sears is still good enough. Spend your money on quality bits and a decent drill will do the job.
By having a pro do the welding you save the learning curve, get a good job and don't have to store or resell the equipment. If you don't know a welder or one you can trust simply call the closest welding supply store and they will likely give you recommendations. I'm pushing this method because welding eats up money. Goggles/masks, gloves, aprons, clamps, benches and alway the potential for injury or fire are all things you don't need for anything else.
Same with files, a good file will last a lifetime, a cheap one won't last at all and won't do a good job. A white or yellow crayon/pencil is imperative as is a good imagination.
BUT, building your own frame is most of the time reinventing the wheel. Unless you have something in mind that can't be modified from an existing frame the easiest and best way is to modify. Building a front end is a special skill and you will still need to buy parts. Watch a couple editions of American Chopper and you'll see what they build and what they buy. These guys are pros and until recently bought their frames and still buy the standard frames. They buy all their front ends.
Good luck, you're facing great challenges, tremendous learning curves and a lot of potential fun. You are already a self taught battery expert and I have confidence you can learn the rest.
Oh, one more thing you'll need. Something I call "stickability". This means when everything turns to shit, and it will, you simply brush off and do it again. One thing I do every time I go into my shop (wood working and automotive home shop) is count my fingers. If I have ten when I go in I try really hard to have ten when I come out.
Oh, still one more thing. Until you have experienced burnt eyes you can't appreciate pain. Welding will burn your eyes. Bad. I've toted several experienced welders in my ambulances who burned them and didn't even know it for several hours. The problem is, for novice welders, is you can't see with the goggles on and don't know where to put the stick. So, you cheat thinking you can get the goggles down before the arc is bright enough to hurt you. Can't be done. Gas or Arc, your eyes will burn. I only have two and want to keep both of them, they are already old and I need them to get older.
Good luck,
Mike