... is doing my mixing and mastering when it is all done. I know it would not be recommended by some engineers (since he most likely uses software instead of hardware for mastering, but he is probably one of my only options. ...
The issue tends to be more about objectivity then the sole use of software. It is very rare to find a mix engineer who is objective enough to be able to master projects that they have mixed even if they leave some time between the two. Someone who places a mix for mastering normally thinks that it is already of sufficient quality and that they have done the best that they can. As such they are not objective enough to critically listen to it.
Unless the engineer has separate studios for mixing and mastering then one or the other or both will end up compromised as the two have different requirements with regard to acoustic treatment and monitor type and placement. I have to say that as a minimum any good mastering engineer should tell you what their monitoring chain - convertors and monitors etc - is if asked. If it's one that is recording/mixing based then be careful. If you can't hear it then you can not master it.
With regard to only using software.
It's quite possible to do good work only using software. Experienced pro mastering engineers however often use hardware as it allows us to get a more natural sound and a wider and deeper stereo stage and so on. Mastering hardware is considerably more expensive than software though. Any mastering engineer who uses hardware is thus also much more likely to have been in the business for some time and have plenty of real experience.
It is also very easy to butcher a project using software. Far too many people claim to be able to master but do little more than use a preset in some software package. Presets don't work in mastering. Software that tends to really be good enough for mastering also tends to be relatively expensive - not as expensive as hardware but more than standard vsts. Much of it is made and sold as individual, specific vsts rather than suites/packages. So you might buy a specific eq or compressor or limiter but you would rarely, if ever, buy them as an 'all-in-one' vst. It's possible to get good results from an 'all-in-one' but you need to spend time using, experimenting and learning what works and what doesn't rather than just use the presets.
Mastering hardware to look out for includes:
Convertors from - Prism, Lavry, Forsell, Mytek, Cranesong...
Monitors from - ATC, PMC, K&H, the Nautillus, Focal, Event, Lipinski...
EQs - Great River, Sontek, Cranesong, Millenia, Gyraf, GML, Maselec, API...
Comps - Maselec, Manley, Millenia, API, Thermionic, Cranesong, Elysia...
... and so on
Software:
Flux, Sonoris, Elephant, Algorythmix...
What tends to be missing in the above are names that are highly regarded in recording/mixing - mastering hardware/software is not the same as recording/mixing.