1. Sure, 3/4hp is more than enough... if you understand you can't use the same size tooling, or speeds and feeds. Welding of debris to the work??? Have you seen an X2 up close? it's a TOY! Sure, it's a toy that does real work, but you are NOT going ro be welding debris to the work piece through the sheer awesome power of an X2. For cutting 4140 and stainless with an X2, if you can't use flood, you have to use mist.
2. It's an X2. It's a toy. Why would you need to bolt it to a 800# bench? A 4" kurt vise dwarfs this machine. How large are the parts you want to machine? How heavy are they? How far will they hang off the table?
3. You want to machine difficult material but you don't want to spend much money? Cannot be done without disappointing you. it can be done, but not for $600 with good results for 4140 and stainless. IF you do ALL the work yourself... Here are somem costs.
1. Ballscrews. $180 and they need to have their ends machined. Don't forget the ball nut mounts.
a. A drive(s) $200-$350 Make sure you have the needed BOB, cabling, E-stop and limit switches
b. A power supply $30-$70 Cheap cheap don't cut it.
c. An old computer and monitor $free to $? Don't forget the PP cable $8-$15
d. motors $38 ea x 3 27s minimum price for what you want. 34s are a waste and actually give less performance. Te 27s you want are $49 ea x 3.
Hardware. If you can get aluminum scrap at work, you have your mounts. If you can't, oy $50 in al at least. Thrust bearings, motor couplings, etc. $100.
Say a total if you do all the work, of $750. For a kit? NWIH