You have a lot of questions that I don't have time now for lengthy answers for all them.
Snails - if you stock snails use only the common pond snail they have thin shells. Snails will play a big part in encouraging fish parasites such as white and yellow grub , black spot disease. Research them. Best ones are in the genus Physa or Physella - several species in this genus. Yellow perch will commonly eat this type of thin shell small snail.
http://www.aquahobby.com/gallery/e_Physa_Snail.phpHybrid BG(HBG) can work well but I don't think just catfish and Yperch (YP) will adequately control the offspring from HBG. If you stock HBG into 0.7ac then after 5-8 yrs I will guarantee you need some type of bass to control them - preferred would be the SMB and add them after the first spawn of HBG. HBG will after several years (5-10yrs) of interbreeding produce a substandard sunfish (mutts) that over the years more and more resemble a mixed genetics green sunfish(GSF). Plan on periodic supplimental stocking of HBG to maintain good numbers of large quality hybrids with the substandard interbreeding mutt sunfish. I would rethink and do more homework for using SMB who will work great and not overpopulate with YP-HBG-crayfish. SMB are not real prolific, easily reducible by angling and not as predacious as LMB. Larger CC eat a lot of 5"-7" perch and HBG. Without proper predation your long term harvest of panfish will be limited to substandard sizes of 5"-7" due to overpopulation problems.
Crayfish can be a big benefit but be very sure you know how to identify rusty crayfish (a Michigan exotic nuisance species, web research it) and never add them because they are aggressive and are not the best fish food for your planed fish species. Papershell crayfish are the very best pond crayfish. Learn to recognize them and stock only them. Many other common stream crays will burrow holes and chimneys into the above water banks.
Fish trees are fish attractors and not fish habitat for small fish. Know the difference. If the pond is not bottom diffused aerated then put fish attractors above the normal pond MI thermocline (6ft). See the thread: Structure, Cover etc in the Archives.
Minnow breeding areas - all water less than 3ft sometimes 1-2ft depending on water level. Consider golden shiners(GS) with FHM. GS do not spawn the same way as FHM.
Turtle raft - Research floating island on this forum. Use Google: pond boss forum floating island. John Monroe and others built great floating structure islands that turtles readily used.
Scan through the Archives for more learning.
http://forums.pondboss.com/ubbthreads.php?ubb=postlist&Board=22&page=1HBG
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=256325#Post256325Plants -
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=440475#Post440475
