The single sided gives better depth of field so if you are placing it on a shelf or somewhere it will only be seen from one side this is the way to go. But if it will be seen form both side like in the center of a table then the double sided will allow everyone to enjoy it.
This print is made to have a tight friction fit and depending on how accurate you printer is it may be to tight. If so a little sanding may be needed on the edges.
Gluing the candles in is not necessary but is recommended as switching them on & off is hard without them falling out of position.
Update: I have now added a retention clip for the LED tealights but if you are using tealights that are larger then the ones indicated below and that do not fit the clips then print the original non clip model and glue in place.
Printing:
I recommend using textured PEI build plate to give the nice textured finish.
Ether print with 0% infill so as light shines through you will not see infill geometry or 100% infill so that light will not shine through.
When printing with PETG i found the top layers where no good so i have included a modifier to have infill just where it is needed to fix this problem. If you are printing in PLA this is not needed and can be deleted by selecting objects tab and then selecting Generic-Cube and deleting it this will save you some printing time and filament.