Max items in an item group

Max items in an item group

What is the maximum please ? (if there is)

& could you please tell me why when I create a new item outside of a group via the api the tax rate is set when I use the following... but when I create a new item inside of a group via the api it isn't ?
Some help on how I make it "Not trackable" & also make it a "service" if required would also be appreciated.

var myarray = {
"item_type": "inventory",
"product_type" : "goods",
"name": myItemName,
"description": "",
"rate": sellfor,
"unit": myUnit,
"purchase_rate": buyfor,
"inventory_account_name": "Inventory Asset",
"purchase_account_name": "Cost of Goods Sold",
"tax_id": "##################",
"group_id": "##################",
"custom_fields" : [{"index" : indexofCustomFieldBay,"value" : "Non stock"}]
}
var options = {
'method' : 'post',
'contentType' : 'application/json',
'muteHttpExceptions' : true
};
var myNewItem = encodeURIComponent(JSON.stringify(myarray));
var url = ' https://books.zoho.com/api/v3/items?authtoken='+token+'&organization_id='+orgID+'&JSONString='+myNewItem;
var response = UrlFetchApp.fetch(url,options);