1. don't know, but I don't think make much differents, because you --> 100% ownership --> LLC --> properties..
2. as to 1mil worth of properties or more per LLC... well, depends, if you looking at cost of structure point of view, more the better, if you looking at liability point of view, less is better, but from tax filing point of view, you should stay under 1mil, because per 1065, if your company value more than 1mil, you must report company balance sheet in tax return to IRS.
3. umbrella, is varies by insurance company, personal policy, will not cover any MFU that is more than 4units( such as a 5plex), but most company will not cover more than 4SFU also.
4. living trust, most people think it can save your estate tax, that is a myth. in theory, living trust can not save you from uncle sam, but it can only save you from probation, and as it self is a seperate entity, you can prolong the estate after you die, if you don't want to distribute all your money at one time. but this is a huge topic, takes 10 books to discuss it.