Agree that money saving expert is probably best for financial advice, especially when threads get tripped up by people making a thing about the OP being male. You'll also get disbelief about your £100k property, because that doesn't exist in the Mumsnet period detached in a naice area in the south east bubble.
Mse has a really good guide for first time buyers which will go through all the mortgage stuff. You'll also be able to download a budget planner, to work out how much money you have available for the mortgage and other bills.
How long do you have to pay for the car and is it a lease where you will need to return the car at the end of the term, or is it a loan or HP agreement where you can keep it after you stop paying? £400 pm is really expensive so something to look at reducing when you are a homeowner.
Do you have a lifetime ISA OP? You can get your savings topped up with one of those, so worth looking into.
Also worth looking at rates Vs deposit as the rate is higher for smaller deposits and lenders are being really cautious at the moment.
I'd probably put more deposit up if I were you. If you have a frugal few months, you might be able to manage 15-20% and get a better rate.
It's probably also a good idea to pay off the PayPal finance and use no other credit products except the credit card and here you should make sure you pay more than the minimum even if it's just a pound a month more. If you pay the minimum, a marker goes on your credit file and banks take this as a suggestion that you are struggling.
They also see other credit products like Klarna etc and possibly PayPal credit as almost akin to payday loans, which are very bad and probably the next financial misselling scandal to blow up over the next couple of years.
How secure is your job OP? That's the other risk, you can get income protection insurance but it can be expensive and have exclusions, so your plan to have savings is also good.
Will the properties you are looking at have room for a lodger if you need extra income to pay the mortgage?