Congratulations on your third, and it's totally normal to feel that mix of emotions lah. I was 36 when my third came and honestly it went fine, though I was definitely more tired than the first two times. Since your parents can't stretch further, a helper really does change the game at this stage of life, especially with two under five still demanding so much.
For choosing a helper, I'd ask about their experience with newborns specifically (can they do night feeds if needed), their approach to the older two (some helpers are better with multiple kids), and be very clear upfront about whether they'll handle laundry, cooking, or just childcare. Some people delegate everything; I kept cooking to myself but had my helper do school runs, laundry, and baby care. It really depends on your family's rhythm. Don't hesitate to ask for references and do a proper trial period.
On logistics, honestly you might find you go out more with a helper, not less, because she can hold the fort while you take the older two out. A third stroller seat isn't essential if your helper can stay home with baby sometimes. For gynae, I had good experiences with the paediatrician-referred obstetricians at KKH, and some private practices near the East Coast have good reputations too. Your first two births abroad might mean you have preferences on pain relief or delivery style that are worth discussing early with whoever you pick.
The pregnancy at 35 is genuinely fine these days, just book your first scan soon to put your mind at ease.
camella