After do this a few years ago i would also look at plinths form over seas they seem to be well made and reasonably priced.
I’d spend more on an arm if I was doing it again, but for the final arm you can getaway with a lesser arm to start. Also consider the 103r is not a modern cart and will required a heavier arm then most modern carts would. The arm is going to be the big spender, that and a proper arm board set up will take time and money to do right. Suggest looking at some arm boards that are round and have the hole off set to allow spindle to pivot changes. Also consider the Garrard’s can sit above or recessed into the plinth this will determine the arm board height or the need for shims etc.
Also consider if your table need restoration that it will not be cheep if your having someone else do it and will most likely require parts. Skimping on the restoration will give you unsatisfactory results, example rumble due to out of round idler. Upgrades can wait, unless your replacing something anyway may as well upgrade it.
IMO setting up a 301-401 for excellent results cannot be done on the cheep so focus on the main stuff now ( base table and plinth-arm board) and put off the stuff like costly carts and arms for a time when you can afford more.
If not done right you wont be happy in the end. They can sound great but if not done right they sound mediocre at best.
I ended up spending upwards of $5k (Canadian) on my restoration with a 12" jelco 750 arm ($850). Expect to spend more over time to sort it out correctly.
In the end I ended up selling mine.