If you want to change fonts for one page then you have to use some custom CSS in your required page header code injection. Please use those code in your required pagae header code injection.
<style type="text/css">
#block-yui_3_17_2_1_1613558390525_5996 p {
font-family: adobe-caslon-pro !important;
font-size: 1.9rem !important;
color: #00ff3d !important;
}
</style>
}
Yes, you can use squarespace deafult "Twitter Feed" block to show your latest tweet. Also, you can embed your twitter timeline from here => https://publish.twitter.com/#
Thanks
Squarespace has their own "Booking an Appointment" functionalities. You will get the booking option under "scheduling". Also, you can use "https://acuityscheduling.com/" for your booking options.