For the text measurements, I always used the character "0". Persistent storage was always cleared as much as possible before every measurement.
Maximal persistent Text length is most likely 2^16 (65 536) characters. My measurements were moving from 65040 to 65287, so the realistic maximum length is slightly above 65 thousand.
Measurement of 65287 caused a complete crash of persistent data reading, resulting in script crashes just when declaring the persistent - only deleting the profile helped there.
I'm not able to tell if these values can be understood as bytes. I tried putting just ASCII characters and also UTF8 characters and the results were always above 65 thousand, even tho the UTF8 character combination can take more than 1 byte for each character. But I don't claim I'm a text encoding expert either. But if yes, we can say the persistent storage limit is 2^16 bytes (aka 64kB).
Maximum count of elements in arrays of empty Text, Integer and Real seem to be most likely 2^14 (16 384), realistically I got into 16221-16239 range. An array of Vec2 is probably 2^13 (8 192) and the weirdest: an array of Boolean is 2^12 (4 096) for a rather unknown reason. Booleans can be expressed in one byte but in Maniaplanet, they take up more space than a Vec3.

The measurement list ordered from largest to smallest count:
- Text max length: 65040-65287
- Array of empty Text max length: 16239
- Array of Integer max length: 16230
- Array of Real max length: 16221
- Array of 1 char Text max length: 13008
- Array of Vec2 max length: 8106
- Array of Vec3 max length: 5398
- Array of Int3 max length: 5396
- Array of 10 char Text max length: 4645
- Array of Boolean max length: 3940 (can anyone explain why tho? xd)
- Array of 50 char Text max length: 1204
- Array of 10 char Text with 10 char Text key max length: 877
- Array of 1000 char Text max length: 64
After I measured all of these, I ran the Text length measure again, and this time I got a value 64754, 533 less than the very first measure which was 65287. So the persistent variable name surely also takes up space in the persistent storage.
So we can probably tell the list of values in the cleanest way like this:
- Text max length: 2^16 (65 536)
- Array of empty Text max length: 2^14 (16 384)
- Array of Integer max length: 2^14 (16 384)
- Array of Real max length: 2^14 (16 384)
- Array of Vec2 max length: 2^13 (8 192)
- Array of Boolean max length: 2^12 (4 096)
- Array of 1 char Text max length: ?
- Array of 10 char Text max length: ?
- Array of 50 char Text max length: ?
- Array of 10 char Text with 10 char Text key max length: ?
- Array of 1000 char Text max length: ?
- Array of Vec3 max length: ?
- Array of Int3 max length: ?

I may try this later though just in case to see how structs are managed in bytes.
By this data information, we are able to calculate the storage size of each type.
Persistent data sums up in the storage, so if I would have two persistent Text variables with 32 thousand characters, I'm just about to reach the persistent limit. Therefore I highly don't recommend going close to the actual limits I measured with your variables, as the amount of persistent data left differs from each user.
Let me know if you're interested in measuring the limits of metadata (if there are any).
