Long associations of short associations or the inverse, which one should I use?

Question

I don't have enough experiences of using Association or Dataset, and when operating with nested associations I meet the following choices.

Consider a two-level association to store members with several propertys, and Length@member is much larger than Length@property. The member keys will be added/deleted by other functions, while the property keys are fixed.

Question1: Should I use long assoc of short assoc, or short of long? Which one is recommended? (I guess long of short is better.)

To be concrete,

max=100;
level1=4;
level2=10;
data[1]=Association@Table[
    "property"<>ToString@j->
        Association@Table[
            "member"<>ToString@i->Table[RandomInteger[max],RandomInteger[i]],
            {i,1,level2}
        ],
    {j,1,level1}
]

generates a $4\times 10$ association like

<|member1-><|property1->{},property2->{66},property3->{},property4->{58,26,10,49}|>,member2-><|property1->{5},property2->{17},property3->{12,47},property4->{44,82}|>,member3-><|property1->{},property2->{5},property3->{35},property4->{65,67}|>,member4-><|property1->{18},property2->{95},property3->{38},property4->{57,47,64,14}|>,member5-><|property1->{43},property2->{71,43},property3->{},property4->{85,6,75}|>,member6-><|property1->{},property2->{53,21},property3->{},property4->{12,65,83}|>,member7-><|property1->{},property2->{51},property3->{7},property4->{}|>,member8-><|property1->{},property2->{},property3->{41,90},property4->{}|>,member9-><|property1->{},property2->{82,32},property3->{60,94},property4->{73,18,48}|>,member10-><|property1->{},property2->{3},property3->{80,83,78},property4->{37,1,56,66}|>|>

assoc//Dataset

Question1`: Is there a standard/recommended function to Transpose nested associations?

This can be easily done like assoc//Dataset//Transpose//Normal and is discussed before, e.g. Association of Associations : how to permute level 1 and level 2 keys?. But since it's a bit old, what is the current status of this question? Which way is more efficient?

Question2: how to protect Values against modification?

Now the Values are actually list, set or some other data structure. Suppose there are some functions to modify them like add/delete/reset, like

add//Attributes={HoldFirst};
add[assoc_,member_,property_][list_]:=
    Module[{},
        assoc[member,property]=
            Join[assoc[member,property],list];
    ];

I want some Values in assoc to be protected against add, and add should be like

add//Attributes={HoldFirst};
add[assoc_,member_,property_][list_]:=
    Module[{},
        checkProtection[assoc,member,property];
        assoc[member,property]=
            Join[assoc[member,property],list];
    ];

So I need some place to store the protected triplets assoc,member,property and there are at least two choices:

• save them into Values like

assoc["member1","property1"]=<|"data"->mylist,"protected"->True|>

In this way assoc is a three-level association.

• save them into a new symbol like

protected//Attributes={HoldFirst};
protected[assoc]^={{"member1","property1"},...}

Which one is better?