Questions - Need some input

hey guys soo ive been doing weekly 5 gallon water changes on my 65 gallon tank and the nitrates have been slowly creeping up and now they are getting way to high at 20ppm tested today.

I am planning on getting a biopellet reactor in december just a little short on cash right now.

Can anyone give me any advice on how many gallons i should be changing on a weekly or monthly basis??

Can i use an Eheim 2217 for temporary filtration until i get my sump built?

We have a 90g aquarium at work that is more than 17 y/o that the silicone is showing it's age and has algae that has managed to grow between it and the glass in the corners. Can we use a razor blade to remove the old silicone and reseal the corners without compromising the structural integrity?

I am building a frag tank out of 1/4" acrylic, the dimensions will be 14"x14"x6". The frag tank will sit on top of my sump and the light that is shining into the frag tank will shine through the tank into the refugium. My question is what size pump should I use for pumping water up from the sump? Also what is the ideal spot to put the output and over flow for maximum flow?

here is a picture of my plan

as the weather starts to get colder and the leafs begin to fall im beginning to dread winter, here most of the power lines are underground but we still get our fair share of power outages lasting a couple hours on average, this year I’m considering buying a UPS to protect my investment, im just wondering if anyone uses one? i was looking at TigerDirect and they have tones, at all different ratings and prices...sort of overwhelming