I need to set up Selesforce

We purchased Salesforce a couple of months ago and in the process of customising it for our organisation (about 10 sales people and 150 employees). We would like to customise it by creating additional fields (about 60), adding new services and customised way of pricing them, and one new object that would be linked to Accounts and Opportunities.
Can you please let me know if you have the relevant experience? If so, what was the largest salesforce project that you've done?

Also can you please let me know your availability in January?

Many thanks,
Natalia