Olly - brazing can be done without lugs and is plenty strong enough for any type of frame - from kids bikes to car chassis (arguably better in fatigue than any other joining method).
You don't actually need a jig - some people just work from a flat surface. Jigs make things much easier, but it can be quite frustrating having to spend time making one before you even start on a frame (but time well spent). As a hobbyist, for tacking together seat stay sub assemblies I still use a big block of wood and nails.
Probably best not to start the engineer / fabricator debate
I started framebuilding to make things that couldn't be bought - compared to buying an off the shelf frame it is pretty expensive / scary if you sit down and honestly add up EVERYTHING that you spend.
If you really want to do it then don't get too obsessive about alignment - if it visually looks ok and the wheel sits central in the stays then it will ride just fine. More important to do a sound structural job. Mike Burrows famously says he has (deliberately) never made a frame where the front and back wheel are in line.
So come on then - of all the posters, what have we actually built? I'll start with:-
Folding bike - Reynolds 531 and plywood monocoque centre section
Kiddy carrying full suspension bike
E-stay rigid 29er ss (sub 16" stays)
Hardtail 29er ss / geared (16.25" stays)
Purgatory cyclocross bike (no seat tube / saddle)
Teenager balance bike
Older kid balance bike
Numerous repairs and dropout alterations, cable stop additions etc.
Current projects are a CX frame for mrs and 26" hardtail for youngest son's next bike.
For originality and inspiration my favourite builder is Julie Racing Design. Gloriously bonkers frames, beautifully made by a really nice guy:-