How to; Mail server SBS 2003

Dear Sir/Madam,

Currently we have 8 POP accounts, hosted at Network Solutions.
We are working on a SBS 2003 R2
It is annoying that we have to wait 15 minutes before it syncs the email from Network Solutions.

I know that we can divert the email directly to our server. But I've got a following questions, which I am sure someone of you can answer.

- Do I need to configure my own SPAM filter?
- If my server is down, will Network Solutions keep it until our server is online again?
- We have an ADSL connection, not very fast. Speedtest shows this;
Download 380 KByte/sec   -  Upload 50 KByte/sec
I think not ideal to host it on our own?
- Do we have to use the SMTP of Network Solutions or from our ISP?
- Do we need to have a SSL connection for this?

I know the internet connection is slow. This is the only option we've got and the next option would be a fiber connection.
It is a lot more expensive as the price we are paying now for internet, and my boss wants to have good reasons why we should take fiber.

Are their any more things I've forgot, based on the email hosting?

Thank you.

Regards
Joey