Would the futaba 3305 work for a 50 inch cat??? Later on planing to get the 5301 or is this to much??

I wouldn't try my cat to that servo. It's only rated 124 oz/in torque at 6v. I try to use servos that are rated 180-200 oz/in or more...I'm old school and still use the old reliable 1/4 scale servos with metal gears for steering in most my boats.

This is one I use a lot...inexpensive and works well: www.servocity.com/html/hs-755mg_1_4_scale.html

Can I use Hitec servos with a futaba fm 75mhz reciver?? if so what servo should do yje work?

No reason why the Hitec servos wouldn't work with your 75mhz Futaba. Just make sure the pinouts are the same. If you have a system that isn't VERY old, the servo pinouts are universal, so not a problem. From right to left, Black, Red, White.