Hello! I'm Jordan.
Not to worry, the tasks that you have outlined are simple and shouldn't take long to complete. There are a number of plugins that I have used for anti-spam but I'll take a look at what's available now as I haven't had to install one for a few months.
I'm afraid my experience with SQL is minimal, however, there are other plugins from WPMU Dev that I can install, as I'm a member with them and these will purge the marked spamming accounts from the database. I'll look more into this and get back to you with the specifics on how it's done.
How long it will take is dependent on the scope of the work such as how out of date everything is. Additionally, If your theme was custom made for you it may not be able to be updated by me unless it's a child theme. I can find this out for you if you are unsure.
Please let me know if you have any further questions.
Thanks,
Jordan.
P.S. My original bid message may have been sent incomplete, butter fingers! Sorry.