1. External system is doing a pull from Salesforce.

Sample SOAP request to pull data:

<?xml version="1.0" encoding="utf-8"?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:urn="urn:enterprise.soap.sforce.com">
<soapenv:Header>
<urn:SessionHeader>
<urn:sessionId>QwWsHJyTPW.1pd0_jXlNKOSU</urn:sessionId>
</urn:SessionHeader>
</soapenv:Header>
<soapenv:Body>
<urn:query>
<urn:queryString>SELECT Id, Name, BillingStreet FROM Account WHERE Name LIKE '%a%'</urn:queryString>
</urn:query>
</soapenv:Body>
</soapenv:Envelope>

How many querystring tags we can use? I wanted to understand if external system has the capability to retrieve mutiple objects data like can we use multiple query strings e.g.,
<urn:queryString>select id, name from Lead</urn:queryString>
<urn:queryString>select id, name from Opportunity</urn:queryString>

What is the limit of this?

2. External system is updating/inserting in to Salesforce.

<soapenv:Header>
<urn:SessionHeader>
<urn:sessionId><b>QwWsHJyTPW.1pd0_jXlNKOSU</b></urn:sessionId>
</urn:SessionHeader>
</soapenv:Header>
<soapenv:Body>
<urn:update>
<urn:sObjects xsi:type="urn1:Account"> <!--Zero or more repetitions:-->
<urn1:fieldsToNull><b>NumberOfEmployees</b></urn1:fieldsToNull>
<urn1:fieldsToNull><b>Fax</b></urn1:fieldsToNull>
<urn1:Id><b>001D000000HTK3aIAH</b></urn1:Id>
<!--You may enter ANY elements at this point-->
<Name><b>Acme Rocket Supply, Inc.</b></Name>
</urn:sObjects>
</urn:update>
</soapenv:Body>
</soapenv:Envelope>

Can we do multiple operations at a time.,
like updating one object and inserting another object?
Updating and inserting on same object?
What is the limit?

Please let me know the responses.

Thanks,

Babu.