FET Bed Heater Board

[Donziboy2]

So I noticed that the MakerFarm Pegasus 10" ships with a Bed Heater relay board and after doing some reading/thinking found it would not be very helpful in the long run and should be replaced with something better.

The design as I have it below has more then just one use and I can see it being used for many things. It is setup to allow any input voltage (change R3 as needed) 10mA device to control a much larger power device. The best Fets to use would have very low RDSon. The Surface Mounted Fet may not have enough cooling for +20A loads and the TO220 would need a heatsink of some kind.

To facilitate this I have started work on a replacement board design that will allow some customization of the parts.
Right now its set up to use 2 different Opto types and 2 different Fet packages. Slow Transistor type Opto's, Fast gate driver Opto's. Dpak(TO263) and TO220 Fets. I chose the packages for 2 reasons.
1. There is a large number of same pinout devices on the market.
2. They are off the shelf parts that are not hard to get.

HeadBed PCB1.jpgHeadBed SCH1.JPG

My Question for you guys is as follows.
1. Should it be the same size as the existing Relay Board and if so what are the dimensions since I dont have my Pegasus yet.
2. Should it be smaller?
3. Should I make it more specialized(like remove the opto and expect whoever uses it to have there own way of driving it)?
4. From my standpoint the standard slow optos should be more then enough, 1-100kHz switching frequency is more then enough to take care of our needs and it reduces losses due to switching(as long as the slow rise/fall does not increase on/off losses). Should I get ride of the Dip8 Gate Driver and just use the Dip4 Opto Transistors. Or should I do a limited run from Oshpark and pull out my trusty O-Scope and compare the Fast vs Slow opto's?
5. Did I make some huge mistake in this design. (considering I have used both circuits at home and at work they should be fine combined, as long as you dont mix resistors/misplace the dip4)
6. Should I replace the 2 large terminal blocks with screw terminals like these http://www.digikey.com/product-detai...798-ND/2171014

Not sure if this should be in one of the larger forums, but for me its first and foremost for the Pegasus and later on it may be used for other things.

Edit
Just noticed I put C1 wrong, should go to pin8 on U2 and GND.
I tried replacing the 2 terminal blocks with those screw terminals. They are kinda big lol. Might make good heatsinks.


Update......

HeadBed PCB8.jpgHeadBed PCB7.jpgHeadBed SCH2.JPG