Ferdco is the home of the Ferdinand Bull and other models - they have often been rated the top of the line by leather crafters who use such "modern" equipment

. They're Mini-Bull is a fine machine, and maybe right up your alley. They also offer a lease option and sell used equipment.
All of the brands listed above (including Artisan which Robert spelled wrong

) will stand you in good stead - but be sure you get an industrial rated machine not a home sew. While many heavy duty home sew machines can and will handle fairly heavy leather, using the proper needles, they are not designed for continuous heavy work.
Considering what you are planning on using it for I'd look for a good flat bed machine with a 5/16" to 3/8" lift which will handle the lighter weight leathers, say up to two to three layers of 4/5 oz just fine. The harness type machines, usually with lifts of 7/16" or more, don't normally do as good a job with the lighter weight leathers.
Google industrial sewing machines, used heavy duty sewing machines, etc. as there are several vendors who offer excellent values on used and re-furbished machines. Also I would check on availability of parts since some of the older Singers and such from the early part of the 20th century are great machines but when parts go you can get stuck big time.
Suggestion would be to call somebody like Ferdco and/or Artisan and let them know what they would recommend for your proposed usage. Be careful - buying sewing machines can get addictive to tool knutz...........