full axle replacement help

[McConnell6531]

Hey Guys, Im out of Surprise, Az.

So Spindle replacement is gonna be too expensive(35-50 per spindle axle and 65 an hour). So I am looking into getting an entire new axle for my trailer. Online prices are above and below $200

What i need to know is how can I be sure that i have the proper size axle, both in length and weight capacity? Is there any defining difference between axle styles ex. square, round, rectangle? Would I be a fool to purchase an axle that is meant for a heavier trailer and boat if its the same size?

and finally any input on axle brand or retailer?

Thanks for the time and help

-Patrick

P.s. And should I do new spring leafs while i am at it?

the trailer suspension and axle is original from '82