My thoughts,
You asked for needs not wish list stuff as several items mentioned above would be very very very nice to have. Just remember there are millions ways to skin a cat but only one way works for you. So here goes.. If you have questions ask away many here weld professionally I believe so someone will answer you with the right info but be mindful. The saying goes "Trust But Verify".
Cypher
Things you need and might like to have:
You said you have a helmet, gloves, 4.5” grinder do you have sleeves
http://www.amazon.com/dp/B0035X8L96/?tag=atomicindus08-20 or
http://www.amazon.com/dp/B00AF8XG4E/?tag=atomicindus08-20 ( always wear cotton clothes when welding) and boots and never wear a wind up watch you like. Do you have a hat for under the helmet
http://www.amazon.com/dp/B00BMGU35I/?tag=atomicindus08-20 helps with sweating etc. The sleeves prevent burns from sparks, slag or the inadvertent lean or reach across a fresh weld. I try to keep my welding tools separate from my regular stuff as they tend to get burns, magnetized and such.
1. 1: Safety glasses for chipping and grinding etc. ( ER Trips for metal in the eye **** and ruin your weekend)
2. 2: Ear Protection (Muff Style) plugs are ok for a quick job but anything long term use muffs Ehh What was that ??? LOL .
http://www.amazon.com/dp/B0017YEMPM/?tag=atomicindus08-20
3. Fire Extinguisher ABC minimum If you plan on welding flammable metals get a D rated one they are $$$$ .
4. Chipping Hammer or Ball Pein, center punch and Wide Cold Chisel you’re going to have slag no way around it when you’re learning and even afterward center punch before drilling to prevent walking.
5. Small Pair of Linesmen pliers .
http://www.amazon.com/dp/B00004SBD4/?tag=atomicindus08-20
6. Tape measure your preference , Soap stone marker
http://www.amazon.com/dp/B002ACOXT0/?tag=atomicindus08-20 Square
http://www.amazon.com/dp/B00002X2HG/?tag=atomicindus08-20 Speed Square
http://www.amazon.com/dp/B00002255O/?tag=atomicindus08-20 Angle finder
http://www.mscdirect.com/product/details/78962602 Machinist Square
http://www.mscdirect.com/product/details/79267969?item=79267969&fromRR=Y Combination Square set
http://www.amazon.com/dp/B0000DD4HZ/?tag=atomicindus08-20 would replace the angle finder and machinist square and such (These Are In Order of preference all come in handy)
7. Wire Brush Long Handle works add A Block Brush or Butcher Brush. (keeps your hands away from fresh welds they tend to be a bit warm :}
http://www.blacksmithsupply.com/catalog.aspx?DeptID=148106&Merchant=Blacksmith_Supply
8. Beware of welding metal with paint or oil and especially galvanized metal the first two could make you ill and or set the coatings on fire, galvanized will make you very ill if not done with venting and respiration protection.
http://www.sperkoengineering.com/html/articles/WeldingGalvanized.pdf
9. Clamps I prefer Vise grip style for most things
http://www.sears.com/irwin-industri...-SPM2042883014?prdNo=1&blockNo=1&blockType=G1 but C Clamps are also helpful various sizes.
10. Welding Magnets are very handy though as long as you have some sort of clamp system they are just nice to have.
http://www.amazon.com/dp/B002D37E38/?tag=atomicindus08-20
11. Good Drill with a fractional drill index of 135 Deg Split Tip drill bits
http://www.homedepot.com/p/BLACK-DE...-Point-Titanium-Drill-Bit-Set-15573/204734924 they will walk less get some bees wax if you’re going to do a lot of drilling to cool the drill bit.
http://www.ebay.com/itm/like/251713236395?lpid=82 works for lubing screws too. A 6 fluted countersink works very well for deburring holes.
http://www.browntool.com/Default.aspx?tabid=344&CategoryID=141&Level=a&productid=797
12. Mig Nozzle gel is nice to have to keep things clean
http://www.amazon.com/dp/B0017Z5J1W/?tag=atomicindus08-20
13. In order of preference for cutting Portable Band saw is nice but pricey for a good one and can get into more places , a good Chop saw
http://www.amazon.com/dp/B000HHWWES/?tag=atomicindus08-20 will work for lots of cutting with less chance of a cut wandering if you’re not use to a portable band saw. You can cut with your 4.5” grinder and keep it straight just takes time and practice.
14. Bare metal primer of your choice again nice to have so when you are done cleaning up the welds and such you can hit them quick and move on then they do not rust while the project is in work. This does depend on your environment.
15. If you’re welding inside a garage you will need a fan in a window or the door open with a fan moving air and smoke out. You can also cheat and find an old stove exterior exhaust fan install it and use it as a welding hood.