Reforming will reduce your land force limits and manpower by about 33%. So expect 66K Manpower and 80 forcelimits.
You lose horde ideas on reforming. Enjoy your generic ideas. On top of this, +125% Manpower lets Russia simply laugh at attrition.
It depends. If your India, you have to worry about every single Colonial power going after you due to missions, infact in my Timurids game where I conquered India, I had been DOWed by both Portugal and England. Even European powers get missions in China occasionally, though they are far less likely to attempt them. Of course, there is Ming as well.
My 1.2 game, I was a Westernized Timurids whom owned and controlled all of Samarkand, Yumen, Kashmir, and Beijing trade nodes, with hundreds of thousands of troops, Horde bonuses, and Western tech. The Russians still DOWed me. Given I crushed them but they were able to field a frightening number of troops despite not having central and western siberia. In 1.3 this kind of game would be quite deadly for me, considering that my Westernized Timurids would not be able to field as many troops, wont have the defensive combat bonus in plains/desert, and will be behind in technology because westernization takes longer and is more pricey, well, unless I go mughals but I much prefer the Timurids flag/color to Mughals.