"I am making a dozen fixtures to hold some odd shaped parts and am thinking about welding them instead of screwing them together." Hm.
Are the parts steel, stainless, or copper alloy? Ever think about silver brazing them together? Praactically zero distortion, very strong, and, if done well with fitted machined joints, very accurate, and hold up to temps to 600 F with little loss of strength.
The only inescapable conditions to silver brazing are scrupulous cleanliness, plenty of flux, good local heat control, and application of the silver brazing alloy so that it goes into the joint instead of blobbing up on the exterior.
Make a few practice joints before you go for the gusto.
Getting back to the MIG question, most home machine shops benefit from the presence of welding equipment provided the show owner takes a night course in welding at the local vocational school or community college. MIG is only one of four metal jointing permanent processes handy to the home shop user. Arc, MIG, TIG, and spot. Add to this silver brazing, soft soldering, oxy-acetylene welding, plasma and oxy-fuel cutting and time spent taking a light class pays off very well in your future metalworking versatility and accomplishment.
All those skills might seem a lot ot take on at one bite but over a couple of school quarters you can cover the basics very well. Also you gain new acquaintances and insights into this new world of metal working. Trust me when I say it's all gain and no loss to learn welding/metals joining skills in parallel to your machine shop skills.