Studio XPS 435mt? I've owned one for 10 years. Done numerous mods and replacements. I couldn't really recommend it because it's getting dated pretty quick now. because of several things. Can't update the bios, ram speed is limited to 1300 mhz, i7 920, parts to upgrade are far too few and in some cases, cost above retail. the ddr 3 ram in the 435 is quickly being dated by ddr4.
Windows 10 would probably tax the start up processes and with newer 64 bit programs with multiple features will slow down considerably. Even with an SSD. In fact, the SSD might be the best upgrade for it. The 920 is only running at 2.67 g and even if you upgrade the motherboard, you're not going to get more than 3.0 g. Even the psu is too small for it.
To start, you'll need to mod the case for cooling, gut everything, get a new motherboard and processor that runs ddr4 (ddr 4 because ddr3 is being phased out).
Would I do it? Yeah, I would. But I'm a computer nut case, an ex tech, a hobbyist and build my computers. I can't recommend trying to rebuild something that old. If you have some background, that helps. Upgrading something that old and that limited, I can't offer any recommendations. The best thing to do is find a used early model ddr4 (z170 motherboard) machine with an i7 processor (Like a 6700k processor). Then you'll have a very good starting point.
You could bury $500 into it and it'll still have incurable problems.
Sorry I'm not much help but I wish you good luck.