Induction is safer to use as there is no open flame. It will also be more efficient and heat up faster. With induction, you get more precise temperature control as well. Induction is easier to clean. The only downside may be the price and the fact you need to use induction-approved cookware. I am a big fan of induction and suggest investing in one. They cook very well.
Ovens may use different thermostats. Some may pre-heat past 400 by 25 degrees on initial heat up by design to compensate for heat loss. Or a door opening to add food. Some brands heat to precisely 400. If you put a manual thermometer in and read it after it gets to temp on the panel, that will tell you a lot. Rack placement, insulation, and convection fan power are some variables too. But it is very possible to cook slightly differently in 2 ovens at the same temp. Always good to hang a thermometer on the rack you can read through the window to check the exact internal temp.
So happy for you. What is needed is the built in trim kit of you are putting them next to each other and want that stainless trim around it, that is more optional but 99% of all people buy it, What is needed is the “heater kit” called a twins pairing kit. It consists of 2 heating mats one for each unit and a power supply to plug them in. Looks like your purchase says it but to be sure call them and confirm as a trim kit and a pairing kit are two separate items but very possible if you bought the trim they threw it in. Once installed please come back and post a photo!
Both can come as big as 28cubic, even more sometimes. The side by side will keep you more organized with extra shelf space in the freezer. But a bottom freezer can hold wider items, platters, etc. So it’s really hard to answer. Personally, I think in the end, a bottom freezer will hold more as it’s easier to pack things in there with more clearance.
Clean with Vinegar and water periodically, then flush it out. Make sure the area stays dry. Keep a rag in arm’s reach to dry up the dispenser tip and spilled water. Try not to use any harsh chemicals as you are ingesting the water from here.