I do all of my welding with either an old Campbell Hausfeld flux core or a newer Hobart flux core. Both of which make a mess unless you have really clean material and fresh wire.

If you want to learn how to weld without destroying your bike in the process, take a continuing education class. Doesn't have any real world practicality since the course is so short (can't use it to get a job) but you will learn the basics from someone who knows what he is doing.

If you really want a machine for home use, get a dual voltage that can run either flux core or standard solid wire with gas. Preferably one that can handle full grown spools (10#), changing out 1-3# mini spools gets old quick. And use it a lot, the wire corrodes from humidity and flux core types will absorb enough moisture to be completely useless.

I do a lot of bodywork with my flux core, some implement repairs. Anything that is expensive to replace (antique cast iron for example) gets sent to a professional. Bike frames and such go to a local FAA or USCG certified shop. Worth the extra coin to have structural welding done with silicon bronze rod.