It's gotten way to big
Yes, you can trim them. Reducing size is best done in spring or fall. The rest of the year you can lightly prune out yellowing or dead foliage. And you can root the trimmings to make more plants. Here is more info:
https://www.gardeningknowhow.com/houseplants/philodendron/pruning-philodendron-plants.htm
https://www.gardeningknowhow.com/houseplants/philodendron/fiddleleaf-philodendron-care.htm
Just wanted to know how often do I need to water my philodendron?
The most often cited reason houseplants die is overwatering, so keep that in mind. It's best to check the soil before watering, rather than watering on a schedule. In the case of philodendron, wait until the top inch of soil is dry before watering again.
https://www.gardeningknowhow.com/houseplants/philodendron/caring-for-philodendrons.htm
Bought in a yard sale so I don’t know if it will be a tree or vining type or... need to repot so I wonder if I should include a central support.
It is hard to tell exactly what type it is. There are so many different varieties. The heartleaf is usually vining. Just from your photos though it looks like they are growing upright. However, even some of the upright ones get so large they need support. I would start out without support and if it needs one later on you can always add one. Here is care information:
https://www.gardeningknowhow.com/houseplants/philodendron/caring-for-philodendrons.htm
Will it survive? How should I care for it now?
Your only hope is that the roots didn't freeze and it will grow back. Try giving it some water and wait a few days and see if it bounces back at all. If the top growth gets slimy and soft, go ahead and cut it back. Here is more:
https://www.gardeningknowhow.com/plant-problems/environmental/how-to-treat-frozen-plants.htm
https://www.gardeningknowhow.com/houseplants/philodendron/split-leaf-elephant-ear-philodendron.htm
https://www.gardeningknowhow.com/houseplants/philodendron/pruning-philodendron-plants.htm
It is in a totally glass sun room and has been there for decades. In the last year or two it has gotten a new shoot which is now 2 1/2’ tall
The brown and yellow spots indicate bacterial leaf spot. You need to remove the affected leaves to prevent spreading. If most of the leaves are affected, only remove 1/3 of the leaves at a time, doing it in stages.
https://www.gardeningknowhow.com/plant-problems/disease/bacterial-leaf-spot.htm
https://www.gardeningknowhow.com/houseplants/philodendron/brown-philodendron-leaves.htm
What type or number combo should I use I have 10/10/10 Acid /Azalea and Palm tree fertilizer
A balanced fertilizer of 10-10-10 usually works for most houseplants. However, I would not use the one for acid plants.
https://www.gardeningknowhow.com/houseplants/philodendron/caring-for-philodendrons.htm
I had just gotten this plant a few days ago and it was already a bit uncared for when I found it. While I have a bit of plants already Please know I\'m still learning, and none are like this one so I want to find out the best way to help from anyone that has experience. A noticeable spot has formed on one of the smaller leaves and before I makes changes I want to know how to proceed. Thank you for any help!
It is bacterial spot. Determining which one will likely require a microscope, but killing it will be easy.
Most bacterial infections will respond well to fungicides. This article will help:
https://www.gardeningknowhow.com/garden-how-to/info/homemade-fungicide.htm
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
Keep in mind that these plants will tolerate things on the drier side. Let the soil dry out, thoroughly, between waterings. Make sure that the top 1/3 of the soil is completely dry, at least.
https://www.gardeningknowhow.com/houseplants/philodendron/caring-for-philodendrons.htm
(The article poses the question whether your plant is a Philo, or Pothos... Your plant is, definitely, Philodendron.)