Sales of restaruant food/beverages are 13.5%
Any other drink, minerals, alcohol would be 21.5% (NB bottled water is 21.5%)
Your re-sale inputs will be largely 0%. Most foodstuffs, meat, veg etc. are 0%. However some at 13.5% like confectionery and some at 21.5% like ice cream.
Your expense inputs will be a mixture depending on the set up but would include
power,light & heat at 13.5%, phone 21%, insurance (no VAT) maybe leasing 21.5%, advertising Repairs etc.etc.
It is not easy to estimate net VAT payalbe based on sales as it depends on the composition of the inputs. The best thing to do is do the cashflow and do a VAT section at the end, using the rates on the main headings to estimate it.
VAT can be filed ever 2,4,6 or 12 months depending on registration, turnover etc. Revenue will often start new businesses on 2 monthly filing then depending on the level of operations and VAT liability might extend that. VAT is payable by the 19th day of the month following the end of the VAT period or the 23rd of the month if filed online through ROS. (Revenue Online Service)
You can also , once you have an idea of the liability, go on direct debit and file the return annually then.