Where do I start?!

I'd think pass the technical aspects at this point and figure out how long I wanted to keep the RV and how old my children are now. It's been 6 years since your last TT experience and your children have continued to grow. Could at least one of them be of an age where sleeping outside the RV appeals to them more whilst allowing you to clean the bathroom and cook their meals?

As for financing costs, ability to pay......have you looked at a loan calculator? Ton of em online. Value down the road can be found there as well.
HTH