You have to determine price, interest rate, amount down, length of term what repairs the sellers will do if any etc..

Nobody really knows lol But seriously they're going to look at the income and performance of the property to determine value and it's unlikely they're going to loan you more than 75% of the value with no track record. 

I plan to get prequalified but I'd like to know for my own knowledge how they determine the maximum loan amount.

This will determine what kind of strategy you will follow, core, core plus, value add or opportunistic.If you were looking at $100k-$250k of capital I'd say you could be more liberal in your approach but since you are talking about 7 figures I would be alot more strategic about where you park your capital.

The detailed steps that make up closing are: A title search is run just prior to closing to determine if there are any liens or assessments on the title.

If you determine all the competing parks are similar to the subject park, with high vacancy & POH, and your test ads do not receive any evidence of demand, then you'll want to punt on the deal. 

My thoughts are that once you've determined what their motivation is for selling and you've structured the deal to best meet their needs and solve their problem, you want to give them the solution to their problem (your contract AND offer letter explaining the contract) ASAP.

They will do a BPO (broker price opinion) and determine their asking price. 

How does one determine how much is for replanting the field or to control more fields?

I've gotten discourage a couple of times and fell back, but I'm determined to make this work for me.