A very warm welcom to the forum Simon
If you are not fancying cutting all of that steel, I would highly reccomend one of HandyAndy's flat pack chassis kits.
It will save you a great deal of time & will get your build off to a flying start, besides the money saved by not having to buy cutting equipment could be put towards a better quality welder
On the subject of welders, the Clarke 150 amp ones are very popular.
Enjoy your build