I'll respond to your questions and pose a few others for you to think about.
- One or two kids: I have read in some places that one may as well try to conceive twins so that it's one and done and either kid has a sibling. Any thoughts or advice would be appreciated.
Twins is hard if there are 2 of you. I do know someone who had twins as a single mum by choice. She moved in with her brother when they were first born to give some support. If you have no support, stick to one.
(2) Job & Income: currently in a permanent role with a small organisation paying £37k. Job is stressful and I've always felt that I wont want to have a family whilst there as they made me feel uncomfortable the only one time I called in sick in 18months. Should I begin looking for higher paying and more flexible jobs? What are the indicators of these? e.g., >£50k? Hybrid working?
Have a look at your area and see what childcare costs. Childcare is in crisis at the moment and the costs can be eye watering. This might also decide question 1 for you. At best you get a 10% discount for twins.
Working full time with kids alone is hard work. Things to think about are school holidays, child sickness, when you'll get time for yourself, when you'll get time to do stuff around the house.
(3) Savings: currently have about £100k saved.
How much do I need to have saved to give me a head start?
That's a good saving amount - keep going.
(4) Housing: currently have a home in a city that I don't live in. I'm in a fixed mortgage term until next year. So, I'm currently renting a studio in the city where I live and work in. When the time comes to remortgage, do I sell old house and buy a small flat where I currently live? What are the key things I need to consider when buying/ renting a home where I want to raise my child - in terms of the property and the area e.g., safety, green space, schools etc.
Key things are a room each and schools. Trying to minimise your mortgage payments as much as possible / reduce amount of house upkeep.
(5) Support system: I have no friends and family. What do I need to build an alternative support system? How much would I spend on childcare on an average month?
This is going to make things super hard. You'll need good water tight childcare. This will not come cheap. NCT courses will help you to meet some other local parents and you'd need to put the effort into making these friends who will help.
(6) Mobility: I have a car - hatchback. I've been using it for 10years. It's about 13years old. Should I get a replacement car that would be newer, and less likely to be break down? What cars are child-friendly?
A car is useful but it depends if you stay city dwelling.
Other things to think about;
What you will tell them about their conception?
What will the child get out of being your child?
How do you imagine life with a school age child, not just a baby?
What will you do if IVF doesn't work? Do you have a cut off age or point?
What will you do if you die before the child turns 18?