I have really not looked at Unity much, but the questions that come to my mind are:
It certainly seems to me like you should be able to proceed by paying nothing now, later maybe getting just the core pro version, sometime later getting one mobile addon, and only getting the second mobile addon after you start having some income.
- Can the free version be used for commercial purposes?
- If not 1., can existing unreleased closed source code be legally transferred to the commercial pro-version later?
- Is there a free version for Android and iOS?
- How much effort is needed to port between platforms? I know the "native" platform languages and API's are different, but I understand Unity abstracts all of that nearly entirely.
- Assuming 4. is somewhat less than "you really need to be working on all platforms from the very begining", why can you not just develop on Windows on the Free or Pro version until pretty late in development (you have a mobile like OS in Windows 8 if you need that), then get the extra mobile licenses later?
- can you not pick either iOS or Android, and only if you have a successful project consider porting to the other?
- If either 1. or 2., is there actually any feature in the Pro version you really need thats worth that investment?
- If 7. and 3., why would you ever need to get the pro version?
1) Yes you can use it commercially, there is however a limit on your annual turnover (If you had a turnover above $100k the previous fiscal year you're not allowed to use the free version)
2) Yes you can transfer your code and work to the pro version whenever you want.
3) Yes, Android, iOS and Windows phone support is included in the free version
4) It depends, for a simple game there is not much effort at all required (As unity takes care of it and it is unlikely that you'll run into hardware limitations), If you need to use platform specific functionality or adapt your user interface / controls / etc to the platform there will be a bit of work required though and for more advanced mobile projects you will have to test things properly on a wide variety of hardware.
5) You could do that, Windows phone(and blackberry) support is included in the normal free and pro licenses (iOS and Android is only included in the free version, they cost extra in the pro version), you won't be able to test your game on iOS and Android without buying the extra licenses though so if you plan on releasing on both iOS and Android you will save time(and thus money if you are paying professionals to work for you) by getting both licenses from the start.
6) That is an option.
7) There are a whole bunch of features such as dynamic soft shadows, hdr, 3d textures, render-to-texture(required for a huge number of advanced shader effects), IK-rigs and productivity boosting functionality (scriptable asset pipeline, profiling tools, etc) that are cut out from the free version, so if you: A) need some of the cut features to make your game or B) value your own or your employees productivity (Which you would do if you're a professional as time = money) then you should get pro licenses.
8) Even if you don't need or want any of the pro-only features the free version can't be used by any business which had a annual turnover of more than $100k the previous fiscal year (Which basically means that it can only be used by start-ups, hobbyists and some really small and not very profitable companies).
