In answer to your queries…sequentially.
1) The easiest means of determining the installed version of the daemon is through the web admin pages. It is listed in the upper right-hand corner; just below the mt-daapd logo.
2) Registration of the software, per se, is not required. It is open source and is distributed under the GPL. There is some benefit in registering here, at the web site, but it is by no means a requirement. Such is at the discretion of the individual.
3) Ron is best suited to respond to your third question. As chief architect and primary developer, he is the ultimate arbiter in that respect. At present there is no provision for voluntary, financial support.